UC-NRLI 


J 


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m 


GIFT  OF 

PROF.  W.B.  RISING* 


ind 
ol., 
Bed 
kn- 

ols 

its. 


tad 

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ee, 

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~    ~ 

IV.  Sound  and  Light.   8vo. 

—  Complete  in  1  vol.,  8vo.     With  Problems  and  Index. 
Cloth. 


EDUCATIONAL    WORKS. 


. 

Gillespie's  Practical  Treatise  on  Surveying,    Copiously  illus- 
trated.     1  vol.,  8vo. 

Higher  Surveying.     1  vol.,  8vo. 

Graham's  English   Synonymes.      Edited  by  Prof.  Reed,  of 

Pennsylvania  University.     12mo. 
Greene's  History  of  the  Middle  Ages.    12mo. 
Henslow's  Botanical  Charts,  adapted  for  Use  in  the  United 
States.     By  Eliza  A.  Youmans.     Six  in  set,  handsomely 
colored. 

History  Primers.    Edited  by  J.  R.  Green,  M.  A. : 
Greece.     By  C.  A.  Fyffe,  M.  A. 
Rome.     By  M.  Creighton,  M.  A. 
Europe.     By  E.  A.  Freeman,  D.  C.  I.,  LL.  D. 
Old  Greek  Life.     By  A.  J.  Mahaffy.     32mo,  cloth. 
England.     By  J.  R.  Green,  M.  A. 
Frani'C,     By  Charlotte  M.  Yonge. 
Home  Pictures  of  English  Poets. 
How's  Shakespearean  Reader. 
Huxley  and  Tonmans's  Elements  of   Physiology  and    By- 

giene. 

Reightley's  Mythology  of  Greece  and  Rome. 
Krnsi's  Inventive  and  Free-Hand  Drawing. 

Synthetic  Series.     Four  Books  and  Manual. 

Analytic  Series.     Six  Books  and  Manual. 

Perspective  Series.     Four  Books  and  Manual. 

Advanced  Perspective  and  Shading  Series.     Four 

Books  and  Manual. 

Textile  Designs.     By  Prof.  Chas.  Kastner,  Massachu- 


setts Institute  of  Technology.     Six  Books. 

—  Outline  and  Relief  Designs.     By  Prof.  E.  C.  Cleaves, 
Cornell  University. 

—  Mechanical  Drawing.      By  Prof.  F.  B.  Morse,  Massa- 
chusetts Institute  of  Technology. 

—  Architectural   Drawing.      By  Prof.  Chas.  Babcock, 
Cornell  University.     Nine  Books. 

—  Machinery.    By  Prof.  J.  E.  Sweet,  Cornell  University. 
(In  preparation.} 

—  Civil  Engineering.     (In  preparation.) 

—  Ceramic  Art.     (In  preparation.) 
Interior  Decorations.     (In  preparation.} 


Latham's  Hand-Book  of  the  English  Language. 
Liddell  and  Scott's  Greek-English  Lexicon.    Abridged. 


CLASS-BOOK 


OF 


CHE  MISTRT 


ON  THE  BASIS  OF  THE  NEW  SYSTEM, 


BY 

EDWARD  L.   YOUMANS,   M.  D., 

ATTTUOB    OK    THE     "HAND-BOOK     OF    HOUSEHOLD    OCIEJiCE.1 
REWRITTEN  AND  REVISED.   WITH   MANY  NJ£W  ILLUSTRATIONS. 


NEW     YORK: 

D.    APPLETON    AND    COMPANY, 
1,    3,    AND    5    BOND     STREET. 

1880. 


C 


ENTERED,  according  to  Act  of  Congress,  in  the  year  1863,  by 

D.  APPLETON  &  CO., 

In  CLo  Clerk's  Office  of  the  District  Court  of  the  United  States  for  the 
Southern  District  of  New  York. 


ENTERED,  according  to  Act  of  Congress,  in  the  year  1875,  by 

D.  APPLETON  &  COMPANY, 
In  the  Office  of  the  Librarian  of  Congress,  at  Washington. 


237382 


PEE  F  A  0  E. 


THE  "  Class-book  of  Chemistry,"  first  published  in 
1852,  was  rewritten  in  1863,  and  has  now  been  again 
thoroughly  revised,  so  as  to  bring  it  into  harmony  with 
the  latest  views,  and  adapt  it  more  perfectly  to  the 
wants  of  those  for  whom  it  was  prepared.  The  first 
edition  represented  the  state  of  chemistry  as  it  pre- 
vailed at  the  time  of  publication,  and  had  been  long  es- 
tablished ;  but  the  revised  edition,  though  adhering  to 
the  old  theories,  recognized  that  they  were  undergoing 
important  modifications.  These  modifications  have 
been  long  in  progress,  and  having  at  length  issued  in  a 
new  system  of  chemical  doctrine,  which  has  been  gen- 
erally accepted  by  chemists,  it  has  been  adopted  in  the 
present  volume,  and  explained  and  applied  as  fully  as 
the  plan  of  the  work  will  allow.  The  present  position 
of  the  science  is,  therefore,  of  special  importance  in. 
relation  to  its  exposition. 

There  can  be  no  question  that  the  new  theories 
mark  an  important  step  in  the  progress  of  chemistry. 
They  harmonize  a  wider  range  of  facts,  and  give  us  a 
more  consistent  philosophy  of  the  subject,  than  the 
theories  they  supersede.  Yet  they  are  far  from  being 
complete.  The  present  situation  is  the  proverbially 


4  PREFACE. 

uncomfortable  one  of  transition  ;  the  old  house  having 
ceased  to  be  habitable,  while  the  new  one  is  unfinished. 
Prof.  A.  Crum  Brown,  of  the  Edinburgh  University, 
in  a  late  address  before  the  British  Association,  well 
stated  the  present  attitude  of  chemical  theory  in  the 
following  words : 

"  It  is  impossible  to  make  a  certain  forecast :  looking  back, 
we  see  a  logical  sequence  in  the  history  of  chemical  speculation ; 
and  no  doubt  the  next  step  will  appear,  after  it  has  been  taken,  to 
follow  as  naturally  from  the  present  position.  One  thing  we  can 
distinctly  see — we  are  struggling  toward  a  theory  of  chemistry. 
Such  a  theory  we  do  not  possess.  What  we  are  sometimes 
pleased  to  dignify  with  that  name  is  a  collection  of  generaliza- 
tions of  various  degrees  of  imperfection.  We  cannot  attain  to  a 
real  theory  of  chemistry  until  we  are  able  to  connect  the  science 
by  some  hypothesis  with  tho  general  theory  of  dynamics." 

This  view  of  chemical  science,  as  a  body  of  thought 
in  process  of  development,  more  perfect  at  present  than 
ever  before,  but  still  imperfect  in  relation  to  the  future, 
should  not  now  be  lost  sight  of.  It  shows  both  the 
reason  and  necessity  of  change,  reconciles  difficulties, 
and  enables  us  rightly  to  estimate  the  value  of  preced- 
ing systems,  which,  although  now  displaced,  were  essen- 
tial conditions  of  chemical  advancement.  We  are  not 
to  regard  past  theories  as  mere  exploded  errors,  nor 
present  theories  as  final.  The  living  and  growing  body 
of  truth  has  only  moulted  its  old  integuments  in  the 
progress  to  a  higher  and  more  vigorous  state.  It  is  cer- 
tainly desirable  that  this  complexion  of  the  subject 
should  be  recognized  in  its  presentation  to  ordinary 
students.  Practical  text-books,  intended  for  mastering 
the  subject  experimentally,  must,  of  course,  be  much 
confined  to  existing  facts  and  the  principles  by  which 
they  are  now  interpreted ;  but  books  designed  to  present 


PREFACE.  5 

the  science  in  its  general  relations  for  popular  educa- 
tional uses  should  not  overlook  the  considerations  sug- 
gested in  the  above-quoted  passage.  In  this  volume, 
therefore,  I  have  aimed  to  preserve  somewhat  the  tran- 
sitional aspect  of  the  subject,  so  that  the  "  New  Chem- 
istry "  may  neither  be  regarded  as  an  ingenious  device 
of  yesterday,  nor  as  a  finality  to  be  acquired  with  no 
expectation  of  further  improvement. 

To  prevent  misconception  respecting  the  claims  of 
this  class-book,  it  is  necessary  to  repeat  what  was  said 
in  the  Preface  to  the  preceding  edition.  It  is  not  de- 
signed as  a  manual  for  special  chemical  students.  It 
aims  to  meet  the  wants  of  that  considerable  class,  both 
in  and  out  of  school,  who  would  like  to  know  something 
of  the  science,  but  who  are  without  the  opportunity  or 
the  desire  to  pursue  it  in  a  thorough  experimental  way. 
Some  acquaintance  with  the  subject  is  now  required  as 
a  part  of  every  good  education ;  but  books  designed  for 
laboratory  use,  and  abounding  in  technical  details,  are 
ill-suited  to  those  who  do  not  give  special  and  thorough 
attention  to  the  subject.  I  have  here  attempted  to  fur- 
nish such  an  outline  of  the  leading  principles  and  most 
important  facts  of  the  science  as  shall  meet  the  needs  of 
the  mass  of  students  in  our  high  schools,  seminaries,  and 
academies,  who  go  no  further  with  the  subject  than  to 
study  a  brief  text-book,  with  the  assistance  perhaps  of 
a  few  lectures,  and  the  observation  of  some  accompany- 
ing experiments. 

The  present  edition  has  been  much  reduced  in  com- 
pass, both  by  the  use  of  larger  type  and  fewer  pages, 
and  it  has  thus  been  brought  into  more  manageable 
limits  for  school-use.  Much  new  matter  has,  however, 
been  introduced  under  various  heads.  The  rapid  devel- 
opment of  spectrum  analysis  since  the  former  edition 


6  PREFACE. 

was  published,  and  the  great  interest  of  the  subject,  have 
led  to  considerable  expansion  of  that  topic.  The  treat- 
ment of  the  chemistry  of  light  is  also  amplified,  and 
the  chapter  on  theoretical  chemistry  explaining  the  new 
system  is  made  as  full  as  the  proportions  of  the  volume 
will  allow.  Tables  of  the  French  system  of  weights 
and  measures  are  appended  for  the  use  of  those  who 
desire  to  employ  it.  As  the  progress  of  investigation 
is  constantly  bringing  physics  and  chemistry  into 
closer  relations,  the  division  of  chemical  physics  has 
been  retained,  although  the  text  has  been  much  reduced. 

Such  a  class-book  can,  of  course,  have  little  value 
for  the  usual  purposes  of  reference.  It  must  be  but  a 
brief  compend  of  general  principles  and  descriptions 
of  some  of  the  most  important  substances,  and  is  not  to 
be  judged  by  the  fullness  of  its  details.  Such  are  already 
the  vast  proportions  of  the  science,  and  such  the  enor- 
mous rapidity  of  its  growth,  that  nothing  less  than 
works  of  encyclopedic  scope  have  value  for  general 
consultation.  Watts' s  invaluable  "  Dictionary  of  Chem- 
istry," with  its  five  volumes  averaging  a  thousand 
closely-printed  pages,  has  already  a  thousand-paged  sup- 
plement ;  and  it  would  require  such  a  volume  every 
year  adequately  to  report  the  progress  of  the  science. 
The  class-book  should  be  supplemented  by  some  such 
ample  treatises  in  every  school-library. 

I  have  to  acknowledge  especial  indebtedness  in 
preparing  the  chapter  on  theoretical  chemistry  to  the 
admirable  volume  of  Professor  J.  P.  Cooke,  entitled 
"  The  New  Chemistry  " — one  of  the  finest  pieces  of 
exposition  in  the  language.  It  is  a  book  that  every 
chemical  teacher  should  study,  and  I  would  moreover 
earnestly  recommend  them  to  place  it  in  the  hands  of 
their  classes,  aad  have  them  go  carefully  through  it.  No 


PREFACE.  7 

other  work  that  I  know  of  can  put  them  in  such  thor- 
ough possession  of  the  later  stand-points  of  chemical 
study. 

To  many  teachers  and  superintendents  of  schools 
who  have  been  anxious  for  the  appearance  of  this  re- 
vised edition  of  the  class-book,  my  apologies  are  due 
for  broken  promises  and  a  delay  in  publication  that 
may  well  have  seemed  without  excuse.  I  have  only  to 
plead  that  the  volume  would  have  been  issued  long 
since  but  for  the  failure  of  my  eyesight  from  overwork. 
I  have  been  greatly  aided  in  this  revision  by  my  excel- 
lent friend  Professor  Charles  Froebel ;  and  I  have  also 
to  thank  another  friend,  Miss  Mary  E.  Shaw,  for  effi- 
cient assistance  in  seeing  the  book  through  the  press. 
That  errors  may  have  crept  in  is  probable,  but  I  think 
they  will  not  be  found  serious,  and  shall  be  "glad  to  have 
any  inaccuracies  pointed  out  for  correction  in  future 
editions. 

E.  L.  Y. 

NEW  YORK,  June,  1875. 


CONTENTS 


PAGE 

INTRODUCTION  ........  .11 

PART  I. 

CHEMICAL    PHYSICS. 
CHAPTER  I. 

»  GRAVITY. 

§  1.  Absolute  Mass,  Volume,  and  Weight         ...                    .14 
§  2.  Specific  Mass,  Volume,  and  Weight 17 

CHAPTER  II. 

MOLECULAR  ATTRACTIONS. 

§1.  Minute  Constitution  of  Matter 23 

§  2.  Adhesion  and  Cohesion 25 

§8.  Diffusion 28 

§4.  Orystallizatwn 35 

CHAPTER  III. 

HEAT. 

§  1.  Thermal  Expansion— Thermometers         .....  46 

§2.  Transference  of  Heat 49 

§3.  Changes  of  Molecular  Aggregation  .          .....  54 

§4.  The  Nature  of  Heat Gl 

CHAPTER  IV. 

ELECTRICITY. 

§  1.  Frictional  Electricity 65 

§2.  Magnetism  .  68 


CONTENTS.  ix 

PAGE 

§3.  Voltaic  Electricity       .  .  ...  71 

§  4  Electricity,  Magnetism,  and  Heat         .  ...     76 

CHAPTER  V. 

LIGHT. 

§  1.  Motion  of  the  Radiant  Forces  80 

§  2.  Interference  and  Polarization    .  ...     82 

CHAPTER  VI. 

THE  CHEMISTRY  OF  LIGHT. 

§  1.  The  Chemical  Rays     .          .  - 

§  2.  Photographic  Chemistry  .  •     93 

CHAPTER  VII. 

SPECTRUM    ANALYSIS. 

§1.  The  Luminous  Spectrum       .  .98 

§2.  The  Spectroscope    ...  .                                           .103 

§  3.  Spectral  Lines,  -         105 

§4.  Theory  of  Absorption      .  .110 

§  5.  Spectroscopic  Applications     .  •         116 

PART  II. 
CHEMICAL    PRINCIPLES. 

CHAPTER  VIII. 
General  Character  of  Chemical  Action       .          .  .127 

CHAPTER  IX. 

THEORETICAL  CHEMISTRY. 

§  1.  Theory  of  Atoms  and  Molecules      ......  134 

§  2.  Progress  of  Chemical  Theory 138 

§3.  Theory  of  Atomicity  and  Quantivalencs 141 

§4.  Theory  of  Radicals 148 

§5.  Theory  of  Adds,  Bases,  and  Salts   ......  150 

§6.  Theory  of  Isomerism  and  Allotropism  .  .          .          .          .155 

§  7.  Theory  of  Combining  Volumes        ......  158 

CHAPTER  X. 
THE  CHEMICAL  NOMENCLATURE       .          .          .          .          .          .          .163 


x  CONTENTS. 

PART    III. 
DESCRIPTIVE     CHEMISTRY. 

DIVISION  I.— PERISSAD  ELEMENTS. 

CHAPTER  XL 

PAGE 

HYDROGEN  ......  169 

CHAPTER  XII. 

THE  CHLORINE  GROUP.— CHLORINE,   FLUORINE,  BROMINE,  IODINE. 

§1.  Chlorine  and  its  Compounds      .          .          .          .          .          .          .175 

§  2.  Fluorine         "  "  ......         180 

§  3.  Bromine 181 

§  4.  Iodine 183 

CHAPTER  XIII. 

THE  SODIUM  GROUP.— SODITTM,   POTASSIUM,   LITHIUM,   RUBIDIUM,   CAESIUM. 

§  1.  Sodium  and  Us  Compounds        .          .          .          .          .          .  .184 

§  2.  Potassium       "  "  188 

§  3.  Lithium,  Rubidium,  Caesium 193 

CHAPTER  XIV. 

SILVER— GOLD --BORON. 

§  1.  Silver  and  its  Compounds     .......         194 

§2.  Gold 196 

§  3.  Boron  and  its  Compounds      .......          197 

CHAPTER  XV. 

THE  NITROGEN  GROUP.— NITROGEN,   PHOSPHORUS,   ARSENIC,  ANTIMONY,  BI5MUTH. 

§  1.  Nitrogen  and  its  Compounds      .          .          .          .  .          .  .198 

§  2.  Phosphorus  "  ......         206 

§  3.  Arsenic  "  .......    210 

§  4.  Antimony  and  Bismuth        .......         212 

DIVISION  II.— ARTIAD  ELEMENTS. 

CHAPTER  XVI. 

OXYGEN. 

§  1.  Oxygen  and  its  Compounds       .          .          .          .          .          .          .214 

§  2.  The  Atmosphere  ,  228 


CONTENTS.  xi 

CHAPTER  XVII. 

THE  SULPHUR  GROUP. — SULPHUR,   SELENIUM,  TELLURIUM. 

PAGE 

§  1.  Sulphur  and  its  Compounds 

§  2.  Selenium  and  Tellurium     .  240 

CHAPTER  XVIII. 

COPPER    AND     MERCURY. 

§  1.  Copper  and  its  Compounds 

§  2.  Mercury     "  "  •         242 

CHAPTER   XIX. 

THE  CALCIUM  GROUP.— CALCIUM,   STRONTIUM,  BARIUM,  LEAD. 

§  1.  Calcium  and  its  Compounds        .  •    244 

§  2.  Strontium  and  Barium          .  ....         247 

§  3.  Lead  and  Us  Compounds  -    2^ 

CHAPTER  XX. 

MAGNESIUM  GROUP.— MAGNESIUM,   ZINC,   CADMIUM. 

§  1.  Magnesium  and  its  Compounds 

§  2.  Zinc  and  Cadmium          .  •    251 

CHAPTER  XXI. 

IRON,  MANGANESE,  NICKEL,   COBALT. 

§  1.  Iron  and  its  Compounds        .          .  .253 

§  2.  Manganese,  Xickel,  and  Cobalt    .  -    260 

CHAPTER  XXH. 

CHROMIUM,  ALUMINIUM,   AND  THE  PLATINUM  GROUP. 

§  1.  Chromium  and  its  Compounds        .  •         261 

§  2.  Aluminium     "  "  •    £62 

§  3.  The  Platinum  Group  ...  .265 

CHAPTER  XXIII. 

TIN,  SILICON. 

§  1.  Tin  and  its  Compounds         .                                       ...         266 
§  2.  Silicon  "  967 

CHAPTER  XXIV. 

§  1.  CARBON  AND  ITS  COMPOUNDS         .  270 

§2.  Combustion 279 


xii  CONTENTS. 

DIVISION  III.— ORGANIC  CHEMISTRY. 

CHAPTER  XXV. 

PAGE 

§  1.  Hydrocarbons  and  their  Derivatives  ...  .287 

§  2.  Alcohols ...  292 

§  3.  Saccharine  Bodies       ........  296 

§  4.  Fermentation         .          .                     302 

§  5.  Ethers  and  Aldehydes 305 

CHAPTER  XXVI. 

ORGANIC  CHEMISTRY  (CONTINUED). 

§  1.  Adds 308 

§  2.  Organic  Alkaloids    .             .                    .                   ...  313 

§  3.  Albuminous  Substances     ........  315 

APPENDIX   ..........  320 

QUESTIONS        ..........  326 

PRONUNCIATION  OF  SOME  TECHNICAL  WORDS  AND  PROPER  NAMES  USED 

IN  THIS  WORK        ........  340 

INDEX    .  342 


THE 

CLASS-BOOK  OF  CHEMISTRY, 


INTRODUCTION. 

1.  What  is  meant  by  Science. — Science  is  a  knowledge 
of  the  phenomena  of  Nature.     By  Nature  is  understood 
that  vast   and   diversified   array  of   things   which   exists 
around  us,  and  of  which  we  form  a  part.     The  term  phe- 
nomena means  literally  appearances,  but  it  is  applied  to  all 
the  objects  and  actions  of  the  natural  world  which  we  can 
recognize  in  any  way.     Thus  we  speak  of  celestial  phe- 
nomena and  material  phenomena,  the  phenomena  of  sound 
and  the  phenomena  of  thought.     Natural  things  are  con- 
stantly undergoing  changes.     These  changes  do  not  take 
place    by  chance  or  irregularly,  but  with  inflexible  uni- 
formity.    The  uniformities  of  change  are  termed  laws,  and 
the  whole  system  of  laws  is  known  as  the  Order  of  Nature. 
It  is,  therefore,  the  object  of  science  to  discover  and  ex- 
plain the  laws  and  order  of  natural  phenomena. 

2.  The  Test  of  Science,— Knowledge  grows ;   ordinary, 
loose  information,  is  gradually  developed  into  the  more 
perfect  form  of  science.     The  qualities  of  things  are  first 
studied,  then  their  quantities ;  first  there  is  certainty,  then 
exactness.     As  the  laws  of  Nature  are  regular,  in  propor- 
tion as  we  understand  them  we  can  foresee  their  effects. 
In  the  simplest  science,  astronomy,  we  can  predict  effects 


12  INTRODUCTION. 

thousands  of  years  -to  fc  come.  In  the  more  complicated 
sciences,  prediction  is  less  complete,  and,  as  each  science 
is  perfected,  it  gives  larger  foresight.  Prevision,  or  the 
power  of  seeing  beforehand  what  will  take  place  in  given 
circumstances,  is,  therefore,  the  most  perfect  test  of  science. 

3.  Matter  and  Force. — The  phenomena  of  Nature  pre- 
sent themselves  under  two  different  aspects  called  matter 
and  force.     Whatever  occupies  space,  or   has  weight,  is 
termed  matter,  and  different  kinds  and  portions  of  it  are 
called  substances,  or  bodies.     The  properties  of  matter  are 
the  characters  by   which   its   different   kinds    are  known. 
Thus  iron  is  known  by  one  set  of  properties,  glass  by  an- 
other, and  air  by   another.     A  fundamental  property  of 
matter  is  its  indestructibility.     There  is  no  evidence  that, 
in  the  course  of  Nature,  or  by  the  operations  of  art,  any 
particle  of  matter  either  comes  into  existence,  or  is  annihi- 
lated.    But,  while  matter  itself  remains  imperishable,  all 
its  forms  are  mutable.    Every  substance  is  capable  of  being 
altered  in  form  or  properties. 

Whatever  acts  upon  matter,  to  change  it,  is  called  force. 
Thus  the  force  of  gravity  causes  bodies  to  change  position 
or  fall  to  the  earth ;  the  force  of  heat  causes  metals  to 
melt,  or  change  form,  and  chemical  force  corrodes  them,  or 
changes  their  metallic  nature.  Different  kinds  of  force  are 
convertible  into  each  other,  but  it  is  now  believed  that 
force,  like  matter,  is  essentially  indestructible,  and  only 
changes  its  form.  The  total  amount  of  energy  in  the  uni- 
verse, by  which  matter  is  changed,  is  held  to  be  unal- 
terable. 

4.  Physical  Properties  and  Changes. — Those  various  fa- 
miliar characters  by  which  bodies  are   known — as  color, 
weight,  hardness,  temperature — are  termed  physical  prop- 
erties ;  and  those  various  alterations  of  form  and  quality, 
which  bodies  undergo  without  destroying  their  distinctive 
characters,  are  termed  physical  changes.     Thus  iron  may 
be  cut,  melted,  or  magnetized,  but  it  still  remains  iron. 


INTRODUCTION.  13 

Gravity,  cohesion,  heat,  light=,  electricity,  and  magnetism, 
are  the  forces  chiefly  concerned  in  modifying  physical  prop- 
erties, and  are  therefore  known  as  physical  forces. 

5.  Chemical  Properties  and  Changes. — But  matter  is 
capable  of  undergoing  changes  by  which  its  distinctive 
characters  are  destroyed.     Thus  bright  iron,  when  exposed 
to  damp  air,  is  converted  into  a  brown  rust.     When  vine- 
gar and  lime  are  brought  together,  they  combine,  losing 
their  properties,  and  producing  a  new  and  different  sub- 
stance.    When  wood  is  heated,  in  the  absence  of  air,  it  is 
changed  to  a  black,  brittle  mass ;  if  heated  in  the  presence 
of  air,  it  is  changed  to  invisible  gases  and  ashes.     These 
are  examples  of  the  chemical  changes  of  matter. 

Chemistry  divides  all  substances  into  two  kinds,  simple 
and  compound.  Compound  bodies  are  such  as  can  be  sep- 
arated or  decomposed  into  simpler  parts ;  simple  bodies, 
on  the  contrary,  are  such  as  cannot  be  thus  decomposed. 
Water  is  a  compound,  and  can  be  separated  into  two  in- 
visible gases ;  but  neither  of  these  can  be  again  resolved 
into  different  kinds  of  matter  ;  they  are,  therefore,  ranked 
as  simple  bodies,  or  elements.  Chemical  science  treats  of 
the  composition  of  matter,  of  the  nature  and  properties  of 
its  elementary  pirts,  of  the  compounds  which  may  be 
formed  from  them,  and  of  the  laws  by  which  combination 
and  decomposition  are  governed. 

6,  Chemical  Physics. — No  chemical   change  can   occur 
without   being   accompanied    by    some   kind   of    physical 
change.     So  intimately  are  the  forces  of  Nature  connected, 
that  the  disturbance  of  any  one  is  certain  to  involve  a  vari- 
ety of  effects.     Physical  forces  and  conditions  have  so  pow- 
erful an  influence  over  chemical  actions,  that  some  knowl- 
edge of  them  is  indispensable   to  the  chemical   student. 
Accordingly,  under  the   title  of   "  Chemical  Physics,"  we 
shall  first  treat  briefly  of  those  physical   agencies   which 
are  most  intimately  connected  with  the  subject  of  chem- 
istry. 


PART  I. 
CHEMICAL  PHYSICS. 


CHAPTER    I. 

GEAVITY. 


§  1.  Absolute  Mass,  Volume,  and  Weight. 

7.  The  Measurement  of  Matter. — The  science  of  chem- 
istry is  based  upon  numerical  laws,  and  the  chemist  is  al- 
most always  occupied  in  investigating  quantities,  amounts 
of  matter,  or  amounts  of  change ;  and  this  is  done  by  the 
operations  of  weighing  and  measuring.  The  amount  of 
any  material  body  occupying  space  is  termed  the  mass,  and 
the  quantity  of  space  so  occupied,  the  volume  or  bulk  of 
that  body.  The  process  by  which  the  volume  of  any  body 
is  determined  is  termed  measurement,  and  the  instruments 
used  for  this  purpose  are  called  measures  of  capacity. 
They  consist  of  vessels  of  various  shapes,  always  inclosing 
the  same  or  multiples  of  the  same  amounts  of  space.  The 
units  or  standard  amounts  of  space  to  which  volumes  are 
referred  vary  in  different  countries.  For  ordinary  purposes, 
gallons,  quarts,  pints,  cubic  inches,  cubic  feet,  and  cubic 
yards,  are  most  commonly  used  with  us,  but,  in  making 
scientific  investigations,  the  metrical  scale,  also  called  the 


MASS,  VOLUME,  AND  WEIGHT.          15 

decimal  or  French  scale,  of  measures  is  now  almost  uni- 
versally employed. 

8.  Metrical  Measures. — The  basis  of  the  metrical  sys- 
tem   of  measures  is  the  linear  metre^  a  length   equal  to 
39.368  American  inches.     To  the  decimal  divisions  of  this 
length,  names  composed  of  the  word  metre  and  a  prefix 
formed  from  Latin  numerals  have  been  given ;  and  the  de- 
cimal multiples  of  the  same  standard  are  similarly  made  up 
by  engrafting  Greek  numerals.     The  following  are  the  des- 
ignations: one-tenth  of  a  metre  is  called  one  decimetre; 
one-hundredth,  one  centimetre;  one  thousandth,  one  milli- 
metre ;  and  ten  metres  are  called  one  dekametre,  one  hun- 
dred one  hectametre,  one  thousand  one  kilometre,  etc. 

The  cubic  decimetre,  or  litre,  is  the  unit  most  generally 
used  as  the  standard  of  volume,  but  the  cubic  centimetre  is 
also  very  often  employed.  To  compare  these  measures 
with  one  more  familiar,  it  may  be  remembered  that  one 
litre  is  equal  to  61.016  cubic  inches  or  2.113  pints. 

9.  Gravity. — The  attractive  force  by  which  bodies  are 
drawn  to  the  surface  of  the  earth  is  called  gravity.     It 
acts  between  masses  of  matter 

FIG.  1. 

of  every  kind,  and  at  all  dis- 
tances. The  mutual  attraction 
of  masses  of  matter  has  been 
thus  illustrated  :  A  pair  of  leaden 
balls,  two  inches  in  diameter, 
were  attached  to  the  ends  of  a 
rod,  which  was  suspended  in  the 
middle  by  a  fine  wire  (Fig.  1).  / 
Two  other  balls  of  lead,  a  foot 
in  diameter,  were  placed  upon  a 
revolving  platform,  and,  when 
the  larger  and  smaller  balls  were 
brought  near  together,  they  were 

mutually  attracted,  as  was  shown  by  the  motion  of  the 
rod.     The  force  exerted  did  not  exceed  the  twenty-millionth 


16 


CHEMICAL   PHYSICS. 


of  the  weight  of  the  lesser  ball,  but  was  sufficient  to 
slightly  twist  the  wire,  and  give  rise  to  a  small  oscillatory 
movement.  The  force  of  gravity  is  proportional  to  the 
quantity  of  matter;  that  is,  if  the  earth  had  twice  its 
present  mass,  its  attraction  would  be  doubled,  if  but 
one-half  its  mass,  its  force  would  be  only  half  as  great. 
So  with  any  body  on  the  earth,  the  force  with  which  it  is 
attracted  increases  or  diminishes  in  exact  proportion  to  its 
quantity. 

10.  Weight. — If  a   body,  instead  of  being  allowed  to 
fall,  is  supported,  its  tendency  to  descend  is  not  destroyed. 
It  is  drawn  downward  with  the  same  force,  but,  as  it  is  re- 
sisted, and  at  rest,  the  force  takes  the  shape  of  pressure. 
This  downward  pressure  of  bodies  is  called  their  weight. 
The  weight  of  a  body  is  the  force  it  exerts  in  consequence 
of  its  gravity,  and,  as  this  force  depends  upon  the  quantity 
of  matter,  it  is  clear  that,   if  the  mass   be  doubled,  the 
weight  will  be  doubled ;  if  the  mass  be  halved,  the  weight 
will  be  halved.     Weights  are  therefore  nothing  more  than 
measures  of  the  force  of  gravity  in  different  objects,  and 
we  measure  the  force  to  determine  the  quantity  of  matter. 

11.  The  Balance. — The  instruments  employed  by  chem- 
ists in  weighing  are  balances.     The  chemical  balance  (Fig. 

2),  used  for  analysis,  consists 
of  an  inflexible  bar,  delicate- 
ly poised  at  a  point  exactly 
midway  between  its  extrem- 
ities, from  which  the  scale- 
pans  are  suspended.  Its 
beam  rests  upon  a  fine  edge 
of  hardened  steel,  which  is 
supported  by  a  flat  plate  of 
polished  agate.  This  beam 

The  Chemical  Balance.  .-,,    ,  ,    .,  ,, 

oscillates  toward  the  earth 

just  as  the  rod  in  the  preceding  experiment  oscillated 
toward  the  larger  balls. 


FIG.  2. 


MASS,  VOLUME,  AND  WEIGHT.  17 

12.  Standard  Weights. — The  operation  of  weighing  con- 
sists in  estimating  the  force  with  which  any  given  body  is 
attracted  toward  the  earth  by  comparing  it  with  other 
masses  of  matter  already  weighed  and  marked  according 
to  some  fixed  standard,  as  Troy,  Avoirdupois,  or  French 
weight.     These  standard  scales  are  quite  arbitrary,  there 
being  no  natural  starting-point,  or  unit.     The  grain-weights 
were  originally  grains  of  wheat.     The   scales  established 
in  this  country  are  capriciously  arranged,  while  the  French 
employ  a  decimal  scale,  which,  being  far  more  convenient,  is 
almost  always  used  in  scientific  investigations,  and  is  gradu- 
ally being  adopted  by  different  states  and  countries  as  the 
legal  standard  for  the  transaction  of  ordinary  business. 

13.  Metrical  Weights. — The  French  or  metrical  system 
of  weights  is  based  upon    the   metrical  measures    before 
mentioned.     The  standard  unit  of  the  scale  is  the  weight 
of  one  cubic  centimetre  of  pure  distilled  water  at  the  tem- 
perature of  maximum  density  (39°.2  Fahr.).     The  decimal 
fractions  and  multiples  of  the  scale  are  distinguished  by 
the  addition  of  the  same  Latin  and  Greek  prefixes  already 
mentioned  above,  to  the  name  oi  the  unit.     This  is  called 
the  gramme,  or  gram.      The  gramme  is  equal  to  .15.432 
grains,  and  the  kilogramme  to  22.046  pounds  avoirdupois. 
Tables  of  equivalence  of  French  and  English  weights  are 
given  in  the  Appendix. 

§  2.  Specific  Mass,  Volume,  and  Weight. 

14.  Specific  Volume. — Different  bodies  of  equal  weight 
do  not  occupy  like  amounts  of  space.     Though  a  pound  of 
cork  exactly  counterpoises  a  pound  of  lead,  yet  the  former 
has  a  volume  forty  times  greater  than  the  latter.     By  com- 
paring, therefore,  the  volumes  of  different  substances  with 
the  volume  of  any  one  body  of  equal  weight  taken  as  unity, 
we  may  obtain  their  specific  volumes. 

15.  Specific  Weight  or  Gravity. — Inversely,  also,   dif- 


18  CHEMICAL  PHYSICS. 

ferent  bodies  of  equal  volume  do  not  weigh  the  same. 
Thus  100  cubic  inches 

Pounds.       Grains. 

Of  hydrogen  weigh         .         .         .         .  2.14 

Of  air  "        .         .  .  31 

Of  water  "  .  .         S.604 

Of  iron  "  28.11 

Of  platinum     '•  .         .         .         .         75.68 

Platinum,  the  heaviest  body  we  know,  is  thus  nearly  a 
quarter  of  a  million  times  heavier  than  an  equal  bulk  of 
hydrogen,  the  lightest  of  known  substances. 

If  we,  then,  determine,  not  the  absolute  gravity  of  a 
substance,  but  its  weight  compared  with  another  body  of 
equal  size,  we  obtain  its  relative,  or  specific  gravity.  Any 
solid  substance  when  immersed  in  water  displaces  a  volume 
exactly  equal  to  its  own  bulk,  and,  at  the  same  time,  loses 
a  portion  of  its  own  weight  just  equal  to  that  of  the  vol- 
ume of  water  displaced.  Water,  which  is  found  every- 
where upon  the  globe,  and  easily  purified  by  distillation,  is 
therefore  taken  as  the  unit  of  comparison  for  solids  and 
liquids.  As  variations  of  temperature  alter  the  bulk  of 
bodies,  sp.  g.  is  taken  at  the  standard  of  60°  Fahr.  In 
the  metrical  S3^stem,  the  weight  of  one  cubic  centimetre  of 
water  at  39°. 2  Fahr.  is  equal  to  one  gramme.  The  weight 
of  one  cubic  centimetre  of  any  body  at  that  temperature, 
expressed  in  grammes,  is  therefore  identical  with  its  specific 
gravity. 

For  determining  the  specific  gravities  of  bodies  various 
methods  are  employed,  differing  according  to  whether  the 
body  under  consideration  is  a  solid,  a  liquid,  or  a  gas ; 
whether  it  is  heavier  or  lighter  than  water,  or  insoluble  or 
soluble  in  it. 

16.  Solids  heavier  than  Water. — Fill  a  vessel  with  wa- 
ter (Fig.  3),  and  drop  in  it  a  piece  of  sulphur  which  has 
been  weighed.  A  quantity  of  water  will  then  escape  into 
the  dish  below,  equal  in  bulk  to  the  sulphur.  Weigh  the 


•SPECIFIC   GRAVITY. 


19 


escaped  water  in  the  lesser  vessel.  If  the  sulphur  weighed 
two  ounces,  the  water  will  weigh  an  ounce.  That  is,  the 
sulphur  weighs  twice  as  much  as  an  equal  volume  of  water ; 
its  specific  gravity  is  therefore  two.  The  best  plan,  how- 
ever, is  to  suspend  the  solid  to  the  scale-pan  of  a  balance 
by  a  fine  thread  or  hair,  and  then  counterpoise  it,  or  get 
its  weight  in  the  air.  Immerse  the  suspended  body  in  a 
vessel  of  distilled  water  (Fig.  4),  and,  as  it  weighs  less,  re- 
move weights  enough  from  the  opposite  scale-pan  to  re- 
store the  lost  equipoise.  Now  divide  the  original  weight 


FIG.  4. 


FIG.  3. 


The  Solid  displaces  its  Bulk  of  Water. 


Weighing  a  Substance  in  Water. 


in  air  by  the  loss  in  water,  and  the  quotient  is  the  specific 
gravity  of  the  substance.  For  instance,  a  piece  of  lead 
weighs  in  air  820  grains,  and  loses  in  water  71  grains.  The 
weight  in  air  divided  by  the  loss  in  water  gives  11.5  as  the 
specific  gravity  of  the  lead. 

17.  Solids  lighter  than  Water.— When  the  body  to  be 
examined  is  lighter  than  water,  it  is  first  weighed  and  after- 
ward attached  to  a  piece  of  metal  heavy  enough  to  sink  it, 
and  suspended  from  the  balance.  The  weiglit  of  a  bulk  of 
water  equal  to  that  of  the  piece  of  metal  and  light  body 
together  is  thus  found,  and,  the  operation  being  afterward 
repeated  with  the  piece  of  metal  alone,  the  difference  be- 


20  CHEMICAL  PHYSICS. 

tween  the  weights  of  the  two  bulks  of  water  displaced 
gives  the  weight  of  water  displaced  by  the  light  body. 

18.  Powdered  Solids,— The  specific  gravity  of  any  sub- 
stance in  powder — as,  for  instance,  a  soil — is  obtained  as 
follows :  Counterpoise  a  thousand-grain  bottle  and  weigh 
into  it  150  grs.  of  soil  to  be  tested.     Fill  with  water  and 
weigh  again  ;  water  and  soil  give,  say  1,096  grs.,  150  of  them 
are  soil,  and  946  water  ;  consequently  54  grs.  of  water  have 
been  displaced  by  150  grs.  of  soil.     The  calculation  is  then 
easy,  54 : 1.000 : :  150  :  2.777  sp.  gr.  of  the  soil.     In  practice 
a  precaution  is  to  be  observed.     The  soil  contains  air  among 
its  particles,  which  would  vitiate  the  result.     To  obviate 
this,  fill  the  bottle  but  half  full  of  water  at  first,  and  shake 
it  well  with  the  soil ;  the  air  escapes,  and  the  bottle  may 
then  be  filled  with  water. 

19.  Soluble  Solids. — When  the  substance  to  be  examined 
is  dissolved  by  water,  its  specific  gravity  is  determined  by 
substituting  for  the  water  some  other  liquid  that  does  not 
dissolve  it,  and  the  specific  gravity  of  which  has  been  ac- 
curately established.     The  bulk  of  water  corresponding  to 
the  bulk  of  the  substituted  liquid  displaced  may  be  found 
by  simple  proportion.     The  liquids  most  generally  used  in 
these  determinations  are  alcohol  and  oil  of  turpentine. 

20.  Liquids  and  Gases.— To  determine  the  specific  gravity 
of  liquids,  procure  a  small  bottle,  and  make  a  fine  mark  wilh 
a  file  and  ink  upon  its  neck.     Counterpoise  it  in  the  bal- 
ance.   Fill  to  the  mark  with  distilled  water  at  60°  Fahr.,  and 
weigh  it.     Empty  and  fill  again  with  the  liquid,  the  specific 
gravity  of  wrhich  is  required.     Its  weight,  divided  by  that 
of  the  water,  gives  the  desired  result.     Suppose  the  bottle 
holds  a  thousand  grains  of  pure  water,  it  will  be  found  to 
hold  1,845  grains  of  sulphuric  acid,  which  therefore  has  a 
sp.  gr.  of  1.845.     For  1000  : 1.000  : :  1845  : 1.845.     It  will 
hold  13,500  grs.  of  mercury,  the  sp.  gr.  of  which  is  hence 
13.5  ;  or  1,030  grs.  of  milk,  sp.  gr.  1.03.     In  practice  it  is 
usual   to  employ  a  bottle  (Fig.  5),  holding  exactly  100  or 


SPECIFIC  GRAVITY.  21 

1,000  grains  of  distilled  water  at  60°,  which  shows  the  re- 
sult at  once  without  calculation. 

The  specific  gravity  of  gases  is  obtained  in  a  similar 
manner.  A  flask  or  globe  suspended  from 
the  arm  of  a  balance  is  weighed  when 
empty,  and  again  when  filled  with  air. 
This  gives  the  weight  of  air,  which  is 
taken  as  unity.  Other  gases  are  then  sub- 
stituted for  the  air,  and  their  comparative 
weights  ascertained.  Gases  are  subject  to 
variations  of  density,  not  only  by  altera- 
tions of  temperature,  but  by  changes  of 
atmospheric  pressure;  these  weights  are 
therefore  taken  at  the  standard  barometric  pressure  of  30 
inches. 

21.  Hydrometer,— Take  a  tumbler,  or  a  light,  slender- 
necked  bottle,  loaded  with  some  shot,  and  float  it  in  pure 
rain-water ;  it  will  sink  to  a  certain  depth,  which  may  be 
accurately  marked  upon  the  glass.  If  now  Flo  6 

placed  in  brine  or  milk,  the  mark  will  stand 
above  the  surface ;  the  vessel  not  sinking 
so  deeply  as  before,  because  the  liquids 
are  heavier.  Place  it  in  alcohol,  and  the 
mark  will  disappear  below  the  surface  ;  it 
sinks  deeper  than  at  first,  because  the  li- 
quid is  lighter  than  water.  Instruments 
arranged  on  this  principle,  and  called  hy- 
drometers, are  used  to  measure  the  specific 
gravity  of  fluids.  They  usually  consist  of 
a  glass  stem  (Fig.  6),  terminating  in  a  bulb 
below,  loaded  with  shot  or  mercury,  and 
floating  in  a  narrow  glass  vessel,  contain- 
ing the  liquid  to  be  tested.  Scales  are  fixed  within  the  stem, 
zero  being  the  point  at  which  the  instrument  sinks  in  dis- 
tilled water  at  60°  Fahr.  In  lighter  liquids  it  sinks  deeper, 
and  the  scale  ascends  from  zero.  In  heavier  liquids  it 


22  CHEMICAL  PHYSICS. 

floats  higher,  and  the  scale  is  reversed.  These  scales  are 
arbitrary  and  different  in  the  various  instruments.  Tables 
accompany  them,  so  that  we  see  at  a  glance  the  sp.  gr. 
which  corresponds  to  any  number  upon  the  scale.  Instru- 
ments of  this  kind  are  much  used  by  manufacturers  and 
dealers  to  determine  the  specific  gravity  or  strength  of 
liquors,  syrups,  oils,  lyes,  etc. 

22,  Importance  of  Specific  Gravity.— Specific  gravity  is 
among  the  most  important  of  the  physical  properties  of 
bodies.     It  affords  an  important  means  of  identifying  them. 
The  mineral,  iron  pyrites,  for  example,  is  in  color  almost 
exactly  like  gold,  and  is  frequently  mistaken  for  it.     But  it 
is  at  once  distinguished  by  the  difference  in  specific  grav- 
ity, an  equal  bulk  of  gold  being  nearly  four  times  heavier 
than  pyrites.     So,  if  gold  is  debased  by  alloying  it  with  a 
cheaper  metal,  taking  the  specific  gravity  promptly  detects 
the  fraud.     The  proportion  of  alcohol  in  spirituous  mix- 
tures, the  richness  of  milk,  the  strength  of  various  solu- 
tions employed  in  the  arts,  and  the  identity  and  purity  of 
many  substances,  are  determined  with  more  or  less  accuracy 
by  finding  this  property. 

23.  Density. — Specific  gravity  is  often  confounded  with 
density,  but  there  is  an  important  difference.    The  specific 
gravity  of  a  body  is  the  ratio  of  its  weight  to  that  of  an 
equal  volume  of  some  substance  selected  as  the  standard, 
and  it  implies  no  unit  of  volume  in  the  determination. 
The  density  of  a  body,  on  the  other  hand,  is  the  amount  of 
matter  by  weight  that  it  contains  in  a  fixed  unit  of  volume 
compared  with  some  substance  taken  as  a  standard.    In  the 
English  system  it  is  the  weight  in  grains  of  a  cubic  inch, 
and  may  be  expressed  as  a  ratio  by  comparing  it  to  the 
weight  of  a  cubic  inch  of  water.     In  the  French  system 
density  is  the  weight  in  grammes  of  a  cubic  centimetre. 


CHAPTER   II. 

MOLECULAR    ATTRACTIONS. 

§  1.  Minute  Constitution  of  Matter. 

24.  Its  Interior  Structure. — From  the  force  which  acts 
between  masses  at  all  distances,  we  now  pass  to  the  study 
of  a  class  of  forces  which  only  come  into  play  when  bodies 
are  in  contact.     They  seem  to  pertain  to  the  interior  struct- 
ure of  substances,  and  hence,  before  treating  of  them,  it 
becomes  important  to  refer  to  that  interior  structure,  or 
how  matter  is  believed  to  be  constituted. 

25.  Porosity  of  Matter. — If  we  place  a  little  water  upon 
chalk  or  cloth,  it  disappears ;  in  a  certain  sense  it  pene- 
trates them,  but  it  only  passes  into  vacant  places  termed 
pores.     Not  only  loosely-composed  substances,  as  soil  and 
flesh,  but  wood,  rocks,  stones,  and  even  dense  metals,  have 
the  same  porous  texture.     Liquid  mercury  passes  through 
lead,  and  water  has  been  also  forced  through  the  pores  of 
gold.     Matter  is,  therefore,  held  to  be  universally  porous. 

26.  Motions  of  Internal  Parts.— If  a  closed  India-rubber 
bag,  filled  with  air,  be  squeezed,  it  will  be  compressed  into 
less  bulk — that  is,  the  particles  of  air  will  be  forced  nearer 
together.    If  alcohol  and  water  be  commingled,  the  mixture 
occupies  a  smaller  space  than  did  the  separate  liquids ;  their 
particles  have,  therefore,  approached  closer  to  each  other. 
If  iron  be  hammered,  it  will  be  driven  into  less  compass, 
the  metallic  particles  being  forced  into  closer  relation.     A 


24  CHEMICAL  PHYSICS. 

certain  amount  of  heat  added  to  bodies  in  either  the  solid, 
liquid,  or  gaseous  form,  will  cause  a  certain  aegree  of  ex- 
pansion— that  is,  will  cause  the  constituent  particles  to  re- 
cede from  each  other;  and,  when  the  heat  is  withdrawn, 
the  particles  again  approach. 

27. — It  is  concluded  from  such  facts  as  these  that  mat- 
ter consists  of  exceedingly  minute  particles  which  are 
never  in  absolute  contact,  but  are  surrounded  by  unoccu- 
pied spaces,  in  which  they  are  free  to  move  under  the 
action  of  forces.  These  ultimate  separated  material  points, 
which  are  of  great  minuteness,  are  termed  molecules,  a 
word  signifying  a  small  mass.  To  the  physicist  molecules 
are  not  imaginary,  but  actual  things  -vith  weights  and  mag- 
nitudes, and  which  do  not  change  in  the  physical  transform- 
ations of  matter.  Molecules  play  a  prominent  part  in  mod- 
ern physical  theory ;  and  have  made  familiar  the  phrases 
molecular  attractions,  molecular  forces,  molecular  constitu- 
tion of  mutter.  The  chemical  aspect  of  molecules  will  be 
considered  in  the  chapter  on  Theoretical  Chemistry,  Part  II. 

28.  Divisibility  of  Matter. — The  division  of  matter  may 
be  carried  to  an  amazing  extent.  Gold  may  be  drawn  out 
as  a  coating  upon  silver  wire  until  the  492-thousand-mill- 
ionth  part  of  an  ounce  is  still  visible,  with  its  proper  me- 
tallic color  and  lustre.  It  has  been  estimated  that,  in  a 
drop  of  the  blood  of  the  musk-deer,  such  as  would  remain 
suspended  upon  the  point  of  a  fine  needle,  there  are  one 
hundred  and  twenty  millions  of  globules.  But  these  ex- 
amples of  the  divisibility  of  matter  bring  us  only  to  the 
threshold  of  a  world  of  wonders.  Microscopic  researches 
have  introduced  us  to  a  realm  of  life  peopled  with  animate 
beings,  which  are  born,  grow,  reproduce  their  kind,  and 
die  ;  and  yet  so  minute  that  many  millions  of  them  heaped 
together  would  not  exceed  in  size  a  grain  of  sand. 

We  will  now  notice  some  of  those  forms  of  force  which 
are  exerted  between  bodies  only  when  in  contact,  and 
which  are  known  as  molecular  attractions.  They  are  mani- 


ADHESION  AND.  COHESION  25 

fested  in  the  forms  of  matter,  solid,  liquid,  and  gaseous, 
which  are  known  as  states  of  aggregation. 

§  2.    Adhesion  and  Cohesion. 

29.  Their  Differences, — Though  the  molecules  of  a  solid 
are  separated,  yet  it  does  not  crumble  to  pieces.     They  are 
held  together  by  a  force  which  reaches  across  their  inter- 
stices and  binds  them  in  a  fixed  relation.     When  this  force 
unites  bodies  dissimilar  in  kind,  it  is  called  adhesion.    The 
sticking  of  chalk  to  a  black-board,  of  mortar  to  bricks,  of 
glue  to  wood,  etc.,  are  examples  of  adhesion.      The  same 
force,  when  acting  between  particles  of  the  same  kind,  is 
termed  cohesion.     The  form,  solidity,  hardness,  elasticity, 
brittleness,  malleability,  and  ductility  of  solids,  are  the  re- 
sult of  various  unknown   modifications  of  cohesive  force. 
There  is  also  a  mutual  attraction  among  the  particles  of 
liquids.     In  a  drop  of  liquid,  cohesion  attracts  the  particles 
into  a  rounded  figure,  against  the  influence  of  their  weight, 
which  would  spread  them  out ;  pendant  drops  still  further 
exemplify  the  same  force. 

30.  Adhesion  of  Liquids  to  Solids. — If  a  glass  rod    be 
dipped  in  water,  the  liquid  will  rise  round  it  above  its  level 
in  the  vessel  (Fig.  7),  and,  when  with- 
drawn, it  will  be  wet.     But,  if  the  same 

rod  be  dipped  in  mercury,  there  is  an 
apparent  repulsion  (Fig.  8),  and  the  rod 
when  withdrawn  is  dry.  If  a  rod  of 
gold  be  dipped  in  the  mercury  it  is 
wetted,  or  covered  with  a  mercurial 

The  Glass  Eod  in  Water. 

film.  The  wetting  in  this  case  shows 
an  attraction  between  the  liquid  and  the  solid,  and  that  it  is 
sufficiently  strong  to  produce  adhesion.  But  there  may  be 
attraction  without  wetting ;  glass  is  not  wet  by  mercury, 
and  still  they  are  attracted,  as  may  be  thus  shown.  Suf- 
pend  a  flat,  circular  plate  of  glass  to  the  arm  of  a  bal::t;cr, 


26  CHEMICAL  PHYSICS. 

counterpoise  it,  and  lower  the  plate  (Fig.  9)  over  a  cup  of 
mercury.  No  matter  how  near  the  glass  approaches,  while 
there  is  no  contact,  there  is  no  attraction.  But,  as  soon  as 
thev  are  made  to  touch,  a  slight  adhesion  occurs,  sufficient 
to  lift  a  portion  of  the  mercury  above  its  level  in  the  ves 


FIG.  9. 


FIG.  8. 


Glass  Rod  in  Mercury.  Attraction  of  Glass  and  Mercury. 

sel,  the  amount  of  which  may  be  exactly  measured  by  the 
number  of  weights  required  to  be  placed  in  the  opposite 
scale-pan  to  separate  them. 

31.  Conditions  of  Wetting. — If  the  adhesive  force  of  any 
solid  for  any  liquid  exceeds  half  the  cohesive  force  of  the 
liquid  particles  for  each  other,  the  solid  will  be  wet.    Thus, 
the  adhesion   of  gold  for  mercury  and  of  water  for  wood 
exceeds  half  the  cohesive  force  of  the  mercurial  and  watery 
particles  for  each  other,  consequently  water  wets  wood,  and 
mercury  wets  gold.     But,  if  the  adhesion  of  the  solid  be 
less  than  half  the  cohesion  of  the  liquid,  wetting  does  not 
follow  contact,  as  is  exemplified  by  glass  and  mercury. 

32.  Capillary  Attraction. — If  glass  rods  with  small  aper- 
tures, open  at  both  ends  (Fig.  10),  be  dipped  in  water,  the 
liquid  immediately  rises  through  the  orifices  to  a  height 
which  increases  in  proportion  to  the  smallness  of  the  open- 
ings.    The  same  thing  may  also  be  beautifully  exhibited 
by  placing  two  plates  of  glass  (Fig.  11)  upon  their  edges 
in  a  dish  of  colored  water,  one  end  being  joined,  and  the 
other  slightly  separated.     The  influence  of  the  gradually- 
approaching  sides  of  the  glass  in  attracting  the  liquid  up- 


CAPILLARY  ATTRACTION. 


27 


ward  is  seen  in  the  course  of  the  curve.     From  the  circum- 
stance that  this  effect  is  best  produced  by  tubes  with  very 


FIG.  10. 


FIG.  11. 


Capillary  Tubes. 


Rise  of  Liquid  between  Plates. 


FIG.  12. 


fine  apertures,  the  attraction  that  causes  these  phenomena 
is  called  capillary  (from  capittm,  a  hair). 

33.  Reversed  Capillarity. — If,  now,  a  glass  tube  be 
dipped  in  mercury,  we  have  again  a  disturbance  of  liquid 
equilibrium,  but  the  effect  is  reversed.  The  interior  col- 
umn of  mercury  is  depressed  below  the  outside  level,  and 
its  surface  exhibits  a  convex  shape,  as  seen  in  Fig.  12.  The 
same  thing  occurs  if  the  tube  be  greased  and  dipped  in 
water,  and  in  all  cases  where  the  liquid  cannot  wet  the 
solid.  The  common  belief,  that  depression 
in  this  case  (as  in  that  of  the  glass  and 
mercury)  is  caused  by  repulsion,  is  quite 
erroneous.  We  have  proved  that,  instead 
of  repulsion,  there  is  a  strong  attraction 
between  glass  and  mercury.  The  reversed 
capillary  action  simply  results  from  the 
preponderance  of  the  cohesive  over  the 
adhesive  force. 

each  particle  is  kept  in  place  by  the  mutual 
action  of  all  the  surrounding  particles.  But,  if  a  column 
of  fluid  be  separated  from  the  surrounding  mass  by  inter- 
posing the  walls  of  a  tube,  the  sides  of  which  exert  no 
equivalent  adhesive  for  ce,  the  cohesion  of  the  mass  below 
draws  down  the  upper  and  outer  particles,  and  produces  a 
roundness  or  convexity  at  the  top. 


In    every  body  of   fluid,   Convex  Liquid  Sur- 


28  CHEMICAL   PHYSICS. 

34.  Adhesion  of  Gases  to  Liquids. —  When  a  liquid   is 
poured  from  one  vessel  to  another,  the  gases  of  the  air  ad- 
here to  the  descending  stream,  are  carried  downward,  and 
a  portion  of  them  remain  combined  with  it.    The  force  to  be 
overcome  by  this  adhesion  is  the  elasticity  of  the  gases,  or 
the  mutual  repulsion  of  their  particles.     Pressure  and  cold 
lower  the  elastic  force,  and  therefore  favor  absorption.     As 
the  temperature  rises,  adhesion  is  diminished,  and  hence 
the  readiest  means  of  driving  out  a  gas  from  solution  is  by 
boiling. 

35.  Adhesion  of  Gases  to  Solids.— If   iron  filings    are 
gently  dusted  over  the  surface  of  water,  they  float,  though 
iron  is  eight  times  heavier  than  water.     This  is  because  of 
the  adhesion  and  condensation  of  a  layer  of  air  upon  their 
surface,  which  prevents  the  water  from  wetting  them.     The 
condensed  air  around  the  particles  forais  a  capillary  cavity, 
and  thus  displaces  a  large  volume  of  the  liquid  in  com- 
parison with  that  of  the  solid.     Insects  walk  upon  water 
and  skim  over  its  surface,  because  the  air  adhering  to  their 
feet  forms   capillary  cavities,  and  prevents  them  from  be- 
coming wetted. 

§  3.    Diffusion. 

36.  Diffusion. — Whenever  the  cohesive  force  subsisting 
between  the  molecules  of  any  body  is  exceeded  by  the  ad- 
hesive force  subsisting  between  its  molecules  and  those  of 
another  body,  the  cohesion  of  one  or  both  bodies  is  over- 
come, their  molecules  separate,  and  become  evenly  inter- 
mixed.    The  bodies  in  this  case  are  said  to  be  dissolved  in, 
or  diffused  through,  one  another,  the  process  by  which 
their  particles  become  intermingled  being  termed  diffusion. 
When  diffusion  takes  place  between  bodies  in  unlike  states 
of  aggregation,  one  of  the  two,  under  the  influence  of  ad- 
hesive attraction,  assumes  the  state  of  the  other.     Thus,  a 
solid  or  liquid,  in  order  to  become  diffused  through  a  gas, 
must  first  assume  the  gaseous  state ;  gases  and  solids,  to  be- 


DIFFUSION   OF   GASES. 


29 


FIG.  13. 


come  diffused  through  liquids,  the  liquid  state;  and  gases 
and  liquids,  to  become  diffused  through  solids,  the  solid 
state  of  aggregation.  The  term  diffusion  is  generally  lim- 
ited to  the  molecular  union  or  intermingling  of  bodies  al- 
ready in  a  like  condition  of  aggregation. 

37.  Diffusion  of  Gases. — The  molecules  of  gases  exercise 
upon  each  other  no  cohesive  attraction.     Consequently,  all 
gases   when  brought  in  contact  will  intermix,  or  diffuse 
through  each  other  uniformly,  and   in  all 
proportions,  the  process  setting  in  even  in 

opposition  to  their  specific  gravities.  Thus, 
if  two  jars  be  connected  by  a  narrow  tube 
(Fig.  13),  and  the  lower  filled  with  carbon 
dioxide,  the  upper  containing  hydrogen,  dif- 
fusion takes  place  through  the  narrow  pas- 
sage. The  light  hydrogen  descends,  and  the 
carbon  dioxide,  though  twenty  times  heav- 
ier, rises,  and  they  become  equally  mingled 
in  both  jars.  Our  atmosphere  owes  its  sta- 
bility to  this  principle,  its  constituents 
being  perfectly  intermingled.  The  bane- 
ful products  of  respiration,  combustion, 
and  decay,  instead  of  accumulating,  are 
incessantly  dissolved  away  and  dispersed  Diffusion  of  Gases 
in  the  atmospheric  ocean. 

38.  Rate  of  Diffusion  of  Gases. — All  gases  do  not,  how- 
ever, diffuse  with  equal  facility,     There  is  a  very  simple  re- 
lation between  the  density  of  gases  and   the  rapidity  of 
their  diffusion,  which  is  expressed  by  saying  that  the  dif- 
fusive power  of  gases  varies  inversely  as  the  square  root 
of  their  densities. 

39.  Osmose  of  Gases. — If  a  vessel  be  divided  into  two 
portions  by   a  diaphragm  or  partition  of  dry  plaster  of 
Paris  or  some  other  porous  substance,  and  each  half  filled 
with  a  different  gas,  diffusion  will  immediately  commence. 
The  rate  of  diffusion  is  governed  by  the  law  already  men- 


30  CHEMICAL   PHYSICS 

tioned,  so  long  as  tue  porous  plate  be  very  thin,  but,  when 
the  plate  is  thick,  the  law  observed  is  different.     A  distinc- 
tion must  also  be  carefully  drawn  between  real  diffusion 
through  small  apertures  and  the  apparently  similar  passage 
of  gases  through  membranous  diaphragms,  such  as  caout- 
chouc or  bladder.     In  this  mode  of  passage,  which  is  called 
osmose,  the  rate  of  interchange  de- 
pends partly  on  the  relative  diffusi- 
bilities  of  the  gases,  partly  on  the 
different  degrees   of   adhesion  ex- 
erted  by  the  membrane,  the   gas 
which    adheres    most    powerfully 
penetrating   the   diaphragm    most 
easily.      A   sheet  of   India-rubber 
tied  tightly  over  the  mouth  of  a 
Passage  of  (^e^throu-h  Mem-    wide  -  mouthed  jar   containing  hy- 
drogen is  soon  pressed  inward,  even 

to  bursting.  If  the  jar  be  filled  with  air,  and  placed  in  an 
atmosphere  of  hydrogen,  the  swelling  and  bursting  take 
place  outward  (Fig.  14).  If  the  membrane  is  moist,  the 
result  is  likewise  affected  by  the  different  solubilities  of  the 
gases  in  the  water  or  other  liquid  which  wets  it.  Though 
the  diffusive  power  of  carbon  dioxide  is  small  compared 
with  that  of  air,  yet  it  easily  passes  into  the  latter  through 
wet  bladder.  This  process  appears  to  be  brought  into 
play  in  atmospheric  respiration.  There  is  air  on  one  side 
of  the  moist  lung-membrane,  and  blood  on  the  other ;  oxy- 
gen is  transmitted  from  the  air  to  the  blood,  and  carbon 
dioxide  from  the  blood  to  the  air. 

40.  Diffusion  of  Liquids  and  Solids  through  Gases The 

diffusion  of  liquids  through  gases  is  a  phenomenon  of  com- 
mon observation.  Water,  as  well  as  other  liquids,  at  all 
temperatures,  gives  off  vapors,  which  diffuse  through  the 
air  as  fast  as  they  are  formed.  Solids  in  some  cases  do  the 
same  thing — ice,  for  example,  evaporating  very  fast  when 
in  contact  with  a  current  of  dry  air.  The  law  which  gov- 


DIFFUSION  OF  LIQUIDS  31 

erns  these  diffusions  is  indentical  with  that  under  which 
other  gaseous  bodies  intermingle. 

41.  Diffusion  of  Liquids. — That  the  molecules  of  liquids 
cohere  may  be  seen  in  the  formation  and  persistence  of 
drops.     But,  though  thus  held  together  by  cohesive  force, 
the   amount  of  its   action   in   liquids   is   never   sufficient 
to  unite  large  masses.      The  adhesive  attraction  of  the 
molecules  of  dissimilar  liquids,  on   the  other  hand,  is  in 
many  cases  very  considerable.     Diffusion  of  liquids  through 
each  other,  though  not  universal  as  that  of  gases,  may  be 
observed  in  many  cases.     Thus,  if  a  colored  fluid,  heavier 
than  water — as,  for  example,  ink — be  placed  in  the  bottom 
of  a  tall  glass  jar  filled  with  water,  taking  care  not  to  mix 
the  two  liquids  by  agitation,  they   will,  after  a  time,  be 
found  commingled. 

42.  Rate  of  Diffusion  of  Liquids. — Different    liquids 
under  entirely  like  conditions  diffuse  with  very  unequal  ve- 
locity. According  to  Graham,  who  placed  small 

jars,  filled  with  liquids  to  be  tested,  in  larger  FIG.  is. 
ones  containing  distilled  water,  as  in  Fig.  15, 
and  determined  the  amount  of  the  inner  solu- 
tion that  diffused  into  water  in  a  given  time, 
substances  were  found  to  differ  greatly  in 
diffusibility,  chlorohydric  acid  proving  to  be 
the  most  diffusible.  The  equal  diffusion  of 
several  solutions  took  place  in  the  following 
times :  Chlorohydric  acid,  1  ;  common  salt, 
2.33 ;  sugar,  7 ;  albumen,  49 ;  caramel,  98.  Substances 
thus  tested  are  called  diffusates. 

Diffusion  is  generally  found  to  take  place  more  rapidly 
at  high  than  at  low  temperatures.  It  is  particularly  rapid 
with  solutions  of  crystallized  substances,  like  sugar,  salt, 
etc.,  and  slowest  with  those  of  non-crystalline  bodies,  which, 
like  gelatine,  gum,  etc.,  are  capable  of  forming  jellies. 
The  substances  of  great  diffusibility  have  accordingly  been 
designated  as  crystalloids,  those  of  low  diffusibility  as 


32  CHEMICAL  PHYSICS. 

colloids.  Crystalloid  bodies  form  solutions  which  are  mo- 
bile, the  solutions  of  colloids  are  viscid.  When  solutions 
of  colloids  are  in  contact,  they  hardly  diffuse  through  each 
other,  while  the  solutions  of  crystalloids  not  only  diffuse 
with  rapidity  through  the  solutions  of  other  crystalloids, 
but  also  through  those  of  colloids. 

43.  Osmose  of  Liquids. — When  a  piece  of  moistened 
bladder  is  tied  tightly  over  the  end  of  a  tube  placed  in  a 
vessel  of  water,  and  then  filled  with  alcohol  up  to  the  level 
of  the  outer  liquid,  the  fluid  in  the  tube  will  shortly  begin 
to  ascend,  and  may  rise  to  a  considerable  height  (Fig.  16). 
The  external  water  passes  through  the  membrane  and  mixes 

with  the  alcohol,  while  at  the  same 
time  a  feeble  current  of  alcohol  flows 
the  other  way  and  commingles  with 
the  water.  When  different  liquids 
are  separated  by  a  membrane  in  this 
manner,  the  one  is  transmitted  fastest 
which  wets  the  barrier  most  perfectly. 
D'ltrochet,  who  first  drew  attention  to 
Osmose  of  LiquM.  this  matter,  named  the  inflowing  cur- 
rent endosmose,  and  the  outflowing 
one  exosmose  ;  but  these  terms  are  lately  less  employed, 
and  the  phenomena  are  now  known  simply  as  osmose,  from 
a  Greek  word  signifying  impulsion.  The  osmose  of  liquids 
is  due  partly  to  their  adhesive  attractions  for  each  other, 
and  partly  to  the  difference  of  their  adhesive  attractions  for 
the  membrane  or  diaphragm,  the  pores  of  which  act  as 
short  capillary  tubes. 

44.  Diffusion  of  Gases  through  Liquids,  Absorption,— The 
diffusion  of    gases   through   liquids  is  called  absorption. 
It  is  a  phenomenon  often  noticed,  the  most  common  liquid, 
water,  being  possessed  of  high  absorptive  power.     The 
power  of  absorption  of  liquids  varies  for  different  gases; 
pressure    or  cold    increases  it,  heat  diminishes    it.      The 
effect   of  pressure   is   often   employed   to  induce  absorp- 


SOLUTION.  33 

tion,  as,  for  example,  when  water  is  impregnated  with  car- 
bon dioxide  to  form  the  common  beverage  known  as  soda- 
water.  When  a  mixture  of  different  gases  is  brought  in 
contact  with  a  liquid,  the  absorptive  power  of  the  latter 
for  each  gas  contained  in  the  mixture  will,  however,  be 
only  proportional  to  the  pressure  of  that  gas.  and  not  to 
that  exercised  by  all  the  gases  present. 

45.  Diffusion  of  Solids  through  Liquids.— The  diffusion 
of  solids  through  liquids,  which  is  termed  solution,  is  fa- 
miliarly known.     In  this  case  the  solid,  assuming  itself  the 
fluid  state,  disappears,  mixing  uniformly  with   the  liquid, 
which  remains  transparent.     The  solid  is  then  said  to  have 
been  dissolved  by  it,  and  the  liquid  employed  is  called  the 
solvent.      A  liquid  which    dissolves    one   substance   may 
refuse  to  dissolve  another,  while  substances  insoluble  in 
one  liquid  are   dissolved   in  others.     A  distinction  must, 
however,  be  drawn  between  solution   which  depends  en- 
tirely on  diffusion  and  solution  which   is  owing  in  part  to 
chemical   change.     In  the  former  case,  as  when  sugar  is 
dissolved  in  water,  the  sugar  may  be  again  obtained  in  an 
unaltered  condition  by  the  vaporization  of  the  water,  while 
in  the  latter  instance,  as  when  zinc  is  dissolved  in  sulphuric 
acid,  the  vaporization  of  the  excess  cf  the  solvent  will  not 
yield  the  solid  zinc,  but   an    entirely  different  substance 
known  as  zinc  sulphate. 

46.  Conditions  favorable  to  Solution. — Whatever  weak- 
ens cohesion  favors  solution.     Thus,  by  powdering  a  sub- 
stance, cohesion  is  partially  destroyed  and  the  surface  in- 
creased ;    solution    is    consequently    promoted.     Heat,   in 
most  cases,  contributes  powerfully  to  solution,  its  effect 
being,  as  is  supposed,  to  weaken   cohesion  by  increasing 
the  distance  between  the  particles  of  the  solid  ;  yet  there 
are  marked   exceptions.     Water  just  above  the  freezing- 
point  dissolves  twice  as  much  lime  as  at  the  boiling-point, 
while  the  solubility  of  common  salt  seems  hardly  affected 
by  temperature.     Some   substances  increase  in  solubility 


34  CHEMICAL  PHYSICS. 

regularly  as  the  temperature  increases ;  in  many  cases  the 
solubility  increases  faster  than  the  temperature,  and  in 
others  it  rises  with  the  increasing  heat  to  a  certain  point, 
and  then  declines,  while  the  temperature  continues  to 
ascend* 

47.  Saturation. — A  liquid  is  said  to  be  saturated  when 
it  has  taken  up  as  large  a  quantity  of  a  solid  as  it  can  dis- 
solve; in  which  case  the  force  of  cohesion  between  the 
particles  of  the  solid  is    equaled  by  the  adhesion  of  the 
solid  and  liquid  to  each  other.     The  solvent  power  of  liquids 
varies  much.     Water  is  the  great  solvent,  and  so  general 
and  important  is  its   use   that,  in   speaking  simply  of  the 
solubility  of  a  body,  water  is  always  understood. 

48.  Separation  of  Solids  from  Solution.— If  the  adhesive 
attraction  between  the  solvent  and  the  dissolved  solid  can 
be  overcome,  cohesive  attraction  resumes  its  sway,  and  re- 
unites the   molecules  of  the  solid.     This  change  may  be 
effected  in  various  ways — as,  when  the  solvent  is  removed 
by  evaporation,  or,  when  another  liquid,  having  no  chemical 
effect  upon  the  solid,  is  mixed  with  the  solution.     When  a 
solution  is  evaporated,  the  solid  is  deposited  either  during 
the  process,  or  remains  at  its  close.     The  former  is  generally 
the  case  with  crystalloid,  the  latter  with  colloid  bodies. 
When  the  solid  is   separated  by  the  addition  of  another 
liquid,  the  separation  is  due  to  the  insolubility  of  the  solid 
in  the  liquid  added.     Thus,  if  water  be  mixed  with  a  solu- 
tion of  camphor  in   alcohol,  the  camphor  separates  as  a 
white  cloud,  at  first  rendering  the  liquid  turbid,  but,  after 
some  time,  depositing  on  the  bottom  of  the  vessel.     The 
instantaneous   separation  of  a  solid  from  a  clear  liquid  is 
termed  precipitation,  and,  the  deposit  formed,  a  precipitate. 
As  most  frequently  observed,  however,  precipitation  is  not 
due  only  to  a  reversal  of  solution,  but  also  involves  various 
forms  of  chemical  action. 

49.  Diffusion  of  Solids. — The   cohesive  attraction  sub- 
sisting between  the  molecules  of  any  solid  is  much  greater 


DIFFUSION.  35 

than  the  like  attraction  between  the  molecules  of  liquids. 
Their  molecules  being  so  much  less  mobile,  diffusion  can- 
not take  place  directly  between  solid  substances ;  but,  when 
they  have  been  first  diffused  through  liquids,  and,  the  re- 
sulting solutions  being  mingled  together,  the  mixed  liquids 
are  exposed  to  conditions  under  which  the  solids  are  com- 
pelled to  again  separate  from  the  solvent,  they  will  in 
some  cases  remain  blended  with,  dissolved  in,  or  diffused 
through,  one  another.  This  takes  place,  for  example,  when 
mixed  solutions  of  magnesic  sulphate  and  zinc  sulphate 
in  water  are  evaporated,  and  likewise  with  the  mixed  so- 
lutions of  many  other  salts. 

50.  Diffusion  of  Gases  through  Solids.  Occlusion. — The 
fact  that  gases  adhere  to  solids  has  already  been  noticed. 
Under  some  conditions,  certain  solids  absorb  large  quanti- 
ties of  gases,  which  appear  to  be  truly  diffused  through  the 
mass  of  the  solid.  Thus,  the  metals  iron,  platinum,  and 
palladium,  have  the  power  of  taking  up  various  gases  ;  the 
last-named  metal  is  said  to  be  capable  of  uniting  in  this  way, 
at  ordinary  temperatures,  with  several  hundred  times  its 
own  bulk  of  hydrogen  gas.  Although  not  directly  demon- 
strable by  experiment,  it  is  maintained  that  the  hydro- 
gen, having  undergone  intense  condensation,  must  be  in  a 
state  of  solidity.  This  diffusion  of  gases  through  solids  is 
termed  "  occlusion"  No  phenomena  bearing  the  character 
of  true  diffusions  of  liquids  through  solids  have  so  far  been 
noticed. 


§  4.     Crystallization. 

51. — Under  various  conditions,  and  particularly  when 
bodies  pass  from  the  liquid  or  gaseous  state  to  the  solid 
state,  their  molecules  tend  to  arrange  themselves  in  reg- 
ular geometrical  forms  termed  crystals,  of  which  Fig.  17 
may  be  taken  as  an  example.  The  substances  in  which 
this  tendency  is  marked  are  said  to  be  crystattizable,  and 


36  CHEMICAL   PHYSICS. 

the  process  of  their  formation  is  called  crystallization. 
Many  substances,  however,  do  not  crystal- 
lize. They  are,  in  that  case,  said  to  be  amor- 
phous^ their  molecular  condition  being  dis- 
tinguished as  amorphism.  Water,  salt,  sugar, 
are  examples  of  crystallizable,  gum  and  glass 
of  amorphous  bodies. 

52.  Crystals  in  Nature. — Nature  teems  with 
crystals.  When  it  snows,  the  heavens  shower 
Crystal  of  tnem  down,  and  ice  is  a  mass  of  crystals,  only 
Quartz.  so  blended  that  we  cannot  distinguish  them. 
Geology  teaches  that  the  materials  of  the  globe  were  for- 
merly in  a  melted  state,  so  that  in  the  slow  process  of  solidifi- 
cation the  opportunity  was  offered  on  the  grandest  scale  for 
the  formation  of  crystals.  Hence  vast  rocky  systems  have 
their  constituents  crystallized,  and  are  known  as  the  crystal- 
line rocks.  Metallic  ores  are  nearly  all  crystallized,  and  im- 
mense regions  of  granite  are  but  mountains  composed  of 
crystals,  varying  in  size  from  particles  that  can  only  be 
distinguished  by  the  aid  of  the  microscope  up  to  masses 
sometimes  weighing  several  hundred  pounds. 

53.  Artificial    Crystals. — Crystals   may   be   artificially 
produced  in  various  ways,  as — from  solutions,  by  the  slow 
cooling  of  bodies  ii  a  state  of  fusion,  by  the  condensation 
of  gases,  or  even  by  rearrangement  of  the  molecules  of 
solids.     When  chemical  action  produces  bodies  not  before 
present,  they  very  frequently  make  their  appearance  in  the 
form  of  crystals. 

54.  Crystals  by  Solution. — It  has  already  been  stated 
that  the  solvent  power  of  liquids  for  any  solid  body  is  gen- 
erally greater  at  high  than  at  low  temperatures.     When, 
therefore,  a  hot,  saturated  solution  of  anv  such  substance — 
as,  for  example,  alum  in  water — is  allowed  to  cool,  a  por- 
tion of  the  solid  separates,  and,  in  doing  so,  assumes  the 
form  of  crystals.    The  liquid  which  remains  after  their  forma- 
tion has  ceased  is  called  the  mother-lye,  or  mother-l  'qitor. 


FORMATION   OF   CRYSTALS  37 

55.  Crystals  by  Fusion. — Nearly  all  bodies  when  cooled 
after  melting  take  the  crystalline  form,  though  this   may 
not  be  at  first  perceptible.     The  spaces  left  between  the 
crystals  which  first  form   are  completely  filled  up  by  the 
portions  which  solidify  afterward,  so  that 

fracture  reveals  only  a  general  crystalline 
structure,  as  may  be  observed  in  broken 
cast-iron  and  zinc.     Common  sheet-tin  is 
beautifully  crystallized,  though   it  is  not 
apparent.     If  with  weak  acid  we  wash  off 
the  thin  surface-film  of  metel,  which  had 
cooled  too  rapidly  to  crystallize,  the  struct-      sulphur-Crystals. 
ure  will  be  revealed  of  a  beautiful  feathered 
appearance.     To  obtain   crystals  by  fusion,  the  excess  of 
liquid  must  be  removed  from  around  those  which  are  first 
formed.      In  this  way   beautiful  sulphur-crystals  are  pro- 
duced.    If   a  quantity  of  this  substance  be  melted,  and 
then  allowed  to  cool  till  a  crust  forms  upon  the  surface  and 
sides  of  the  vessel,  crystals  will  be  formed  within,  which 
may  be  seen  either  by  breaking  the  vessel  (Fig.  18),  or  by 
piercing  the  crust  and  draining  off  the  interior  liquid. 

56.  By  Sublimation. — Solid  substances  vaporized  (sub- 
limed) may  be  condensed  in  the  crystalline  form,  as  iodine, 
sulphur,  arsenic.     Camphor  thus  vaporizes  and  condenses 
in  brilliant  crystals  upon  the  sides  of  apothecaries'  jars  by 
the  rise  and  fall  of  common  temperatures. 

57.  Crystallization  in  the  Solid  State.— The  strong  ten- 
dency of  molecules  to  assume  crystalline  shape  is  mani- 
fested even  in  solids.     Thus  sugar-candy,  at  first  transparent 
and  amorphous,  after  some  time  becomes  opaque  and  crys- 
talline.    Glass,  by  long-continued  heat,  though  it  does  not 
melt,  becomes  also  opaque  and  crystalline  (JReaitmur^s  por- 
celain).    Brass  and  silver,  when  first  cast,  are  tough  and 
uncrystalline,  but,  when  repeatedly  heated  and  cooled,  they 
become  brittle,  and  show  traces  of  crystallization.     Even 
the  little  liberty  the   particles  obtain  by  the  motions  of 


38  CHEMICAL  PHYSICS. 

heating  and  cooling  they  improve  to  assume  the  crystal- 
line condition.  Tins  is  still  better  seen  where  the  particles 
of  bodies  are  thrown  into  motion  by  blows  and  vibration. 
Metals,  by  hammering,  lose  their  ductility  and  tenacity, 
and  become  brittle  and  crystalline.  Coppersmiths,  when 
hammering  their  vessels,  frequently  anneal  them,  to  pre- 
vent their  flying  to  pieces ;  that  is,  they  heat  them,  and 
then  allow  them  to  slowly  cool.  Thus  also  bells,  long 
rung,  change  their  tone ;  cannon,  after  frequent  firing,  lose 
their  strength,  and  are  rejected ;  and  so  the  perpetual  jar 
and  vibration  of  railroad-axles  and  the  shafts  of  machinery 
gradually  change  the  tough,  fibrous  w rough t-iron  into  the 
crystalline  state,  weakening  them  and  increasing  their  lia- 
bility to  fracture. 

58.  Crystals  by  Decomposition. — It  is  also  possible,  by 
the    decomposition   or  other  chemical  change  wrought  in 
various  bodies,  to  obtain  substances  not  before  present  in 
the  shape  of  crystals.     Thus,  many  compound  gases,  when 
passed  through  red-hot  tubes,  deposit  crystals,  and  solutions 
of  metallic  salts  are  decomposed  by  the  galvanic  current, 
with  the  separation  of  the  metals  in  the  crystalline  form. 

59.  Phenomena  attending  Crystallization. — This  change 
of  state  is  usually  attended  by  change  of  bulk.     Water  in 
freezing  expands  to  a  considerable  degree,  and  with  great 
power ;  1,000  parts  of  water  are  dilated  to  1,063  parts  of 
ice  ;  and  the  force  exerted  by  the  particles  in  changing  po- 
sitions is  so  enormous  as  to  burst  the  strongest  iron  vessels. 
Heat  is  always  manifested  when  crystals  are  formed,  in 
proportion  to  the  rapidity  of  the  change  from  the  liquid  to 
the  solid  state.     Light  has  also  occasionally  been  noticed 
to  accompany  the  process,  but  its  cause  is  not  explained. 
Muddy  and  impure  solutions  often  yield  the  largest  crystals, 
and  the  presence  of  foreign  bodies  which  do  not  themselves 
crystallize  may  thus  modify  the  form  which  the  crystal  as- 
sumes.    For  example,  common  salt  usually  crystallizes  in 
the  form  of  a  cube  (Fig.  27),  but,  if  urine  be  present  in  the 


CONDITIONS  OF   CRYSTALLIZATION.  39 

solution,  it  takes  the  form  of  the  octahedron.  When  a 
crystal  is  broken,  there  is  a  tendency  to  repair  it ;  it  con- 
tinues to  increase  in  every  direction,  but  the  growth  is 
most  active  upon  the  fractured  surface,  so  that  the  proper 
outline  of  the  figure  is  restored  in  a  few  hours. 

60.  Favorable  and  Unfavorable  Conditions. — Vibratiou 
may  so  disturb  the  process  as  to  check  the  growth  of  those 
which  have  commenced,  and  start  a  second  crop  upon  them. 
Crystals  are  seldom  found  perfect,  being  generally  irregular, 

FIG.  20. 
FIG.  19. 


Crystal  of  Alum.  Masses  of  Imperfect  Alum-Crystals. 

disguised,  and  distorted.  Perfect  alum-crystals,  for  ex- 
ample, are  regular  octahedrons  (Fig.  19),  but  Fig.  20  shows 
how  they  appear  in  the  large  vat  of  the  manufacturer. 
Sometimes  the  attractions  are  so  balanced  that  a  jar  or 
agitation  is  needed  to  start  the  action.  In  a  perfectly  still 
atmosphere,  water  may  be  cooled  eight  or  ten  degrees 
below  the  freezing-point  without  congealing,  but  the  vibra- 
tion of  the  vessel  produces  a  sudden  crystallization  of  part 
of  the  liquid  into  ice.  Any  solid  body  intruded  into  the 
liquid,  by  adhesion,  may  destroy  the  equilibrium  and  begin 
the  play  of  the  crystallizing  attractions.  Thus,  threads 
are  stretched  across  vessels  containing  solutions  of  sugar, 
and  form  a  nucleus  around  which  rock-candy  is  crystal- 
lized. 


40  CHEMICAL  PHYSICS. 

61.  Forms  of  Crystals. — Leaving  disturbing   influences 
out  of  view,  all  liquids  tend  to  assume  the  spherical  shape 
of  drops,     We  might,  therefore,  anticipate  that,  in  return- 
ing to  the  solid  state,  their  molecules  would  still  group 
themselves  round    centres    into    spheres.      But,    although 
something  of  this   kind  may  take  place  with  amorphous 
bodies,  the  forms  produced  in  the  solidification  of  crystal- 
lizable  substances  are  angular,  and  bounded  on  all  sides  by 
plane  surfaces  symmetrically  arranged. 

62.  Elements  of  Crystalline  Form. — Although  there   is 
an  almost  endless  diversity  in  the  forms  which  substances 
take  when  crystallizing,  crystals  are  built  i;  p  in  obedience 
to  universal  geometrical  laws,  and  present  in   the  most 
varied  forms  certain  constant  elements  of  construction.    All 
crystals    are   solids  of    the  class  known    to   geometry  as 
polyhedrons  •  they  are  bounded  by  plane  surfaces,  or  faces, 
which  meet  by  twos  in  stright  lines,  or  edges,  inclosing  be- 
tween them  interfacial  angles.     The  faces,  polygons  in 
shape,  present  three  or  more  plane  angles,  and  three  or 
more  of  these,  having  a    common    apex,   inclose   a  solid 
angle. 

63.  Axes  of  Crystals. — Single  crystals  often  present  a 
large  number  of  faces,  but  the  position  of  all  of  these  bears 
a  fixed  mathematical  relation  to  that  of  the  faces  of  simpler 
forms,  so  that  the  former  may  be  calculated  when  the  latter 
are  known.     These  simple  shapes,  from  which  the  others 
are  said  to  be  derived  by  modification,  are  termed  primary 
forms.     The  primary  forms,  as  usually  assumed,  are  solids 
bounded  by  six  quadrilateral  faces  meeting  in  twelve  edges 
and  eight  solid  angles.     Every  one  of  the  faces  will  be 
opposite   and  parallel  to  another ;    therefore    when  their 
centres  are  connected  by  straight  lines,  these  must  be  three 
in  number,  and  intersect  each  other  in  the  centre  of  the 
primary.     In  some  cases  it  has  been  found  more  convenient 
to  assume  four.     They  are  termed  the  axes  of  the  crystal, 
and  it  is  known  that  all  the  faces  observed  in  any  crystal, 


FORMS   OF   CRYSTALS. 


41 


when  extended  to  meet  them,  will  always  do  so  at- dis- 
tances from  the  centre,  bearing  a  very  simple  numerical  re- 
lation to  the  distances  at  which  they  are  met  by  the  faces 
of  the  primary  form.  The  different  geometrical  elements 
of  crystalline  form  are  thus  mutually  dependent  ;  hence, 
when  a  certain  number  of  these  are  known,  the  rest  may 
be  computed.  Accordingly,  when  it  is  desired  to  deter- 
mine the  position  of  all  the  faces,  the  length  of  the  axes, 
etc.,  of  any  crystal,  all  that  is  required  is  the  measurement 
of  some  of  the  interfacial  angles,  an  operation  performed 
by  the  aid  of  certain  instruments  called  goniometers. 

64.  Systems  of  Crystallization. — All  the  different  crys- 
talline forms  which  have  been  observed  have  been  classified 
and  arranged  in  a  number  of  groups  termed  systems  of 
crystallization.     There  are    six  of  these  systems,  and  the 
forms  belonging  to  each  of  these  differ  from  the  forms  be- 
longing to  the  other  systems,  either  in  the  number  or  the 
relative  length  of  the  axes,  or  in  re- 
gard to  the  angles  which  the  axes 

form  at  their  intersection  in  the  cen- 
tre of  the  crystal. 

65.  Monometric  or  Regular  Sys- 
tem.— In  the  forms  of  this  system 
(Fig.  21)  the  axes  are  three  in  num- 
ber, of  equal  length,  and  intersect 

each  other  at  right  angles.  Crystals  of  this  system  ex- 
pand equally  in  all  directions  by  heat,  and  refract  light 
in  the  ordinary  manner.  Common 
salt  and  iron  pyrites  are  exam- 
ples. 

66.  Dimetric,  Quadratic,  or  Square 
Prismatic  System.  —  In  this  system 
there  are  three  axes  intersecting  each 
other  at  right  angles.  Two  are  equal, 
the  third  is  of  a  different  length.  Its 
forms  expand  by  heat  equally  in  two  directions  only,  and  split 


FIG.  21. 


Regular  System. 


FIG.  '2-2. 


Square  Prismatic  System. 


CHEMICAL   PHYSICS. 


the  ray  of  light  passing  through  them  (double  refraction),  as 
do  also  the  forms  of  the  four  systems  remaining  to  be  no- 
ticed.    Examples :  stannous  oxide  and  mercuric  cyanide. 
Trimetric,  Rhombic,  or  Right  Prismatic  System. — In 


67 


FIG.  23. 


Right  Prismatic  System. 
FIG.  24. 


Oblique  Prismatic  System. 
FIG.  25. 


the  forms  of  this  system,  the  three 
axes  are  also  at  right  angles  to 
each  other,  but  all  three  of  unequal 
length.  Crystals  of  this  system 
(Fig.  23)  expand  unequally  in  the 
three  directions  of  the  axes.  Nitre 
and  topaz  may  be  taken  as  examples. 

68.  Oblique  Rhombic  or  Oblique 
Prismatic  System, — The   forms  of 
this  system  have  three  axes,  which 
may   be  unequal   (Fig.  24).     Two 
are  placed  at  right  angles  to  each 
other,  and  the  third  is  oblique  to 
one  and  perpendicular  to  the  other. 
Sodic  sulphate  and  borax  are  com- 
mon examples. 

69.  Oblique  Rhomboidal  or  Dou- 
bly Oblique  Prismatic  System.— In 
this  there  are  three  axes,  which  may 
be  all  unequal  and  all  oblique  (Fig. 

Doubly  Oblique  Prismatic  System.  35).       Examples  I     CUpHc     sulphate 

and  bismuthous  nitrate. 

70.  Rhombohedral  or  Hexagonal 
System. — The  forms  of  this  system 
(Fig.  26)   differ  from  those  of  the 
others  in  having  fotir  axes,  three  of 
which  are  equal,  in  the  same  plane, 

Khombohedrai  System.  an(j  inclined  at  angles  of  60°,  while 
the  fourth  is  of  different  length  and  perpendicular  to  the 
other  three.  Examples  :  quartz,  Iceland  spar,  and  ice. 

71.  Axial  Polarity. — The  axes  of  crystals  are  not  mere 
imaginary  lines.  The  force  which  builds  the  crystal  works 


FIG.  2(5. 


POLARITY  IN  CRYSTALLIZATION.  43 

unequally,  and  endows  it  with  different  powers  in  different 
directions.  In  those  crystals  where  the  axes  are  all  equal, 
light,  heat,  and  electricity,  are  conducted  equally  in  every 
direction.  But,  where  the  axes  are  unequal,  conduction 
of  heat  and  electricity,  hardness,  elasticity,  transparency, 
expansion  by  heat,  and  luminous  refraction,  are  corre- 
spondingly unequal,  showing  an  actual  difference  of  struct- 
ure in  the  different  directions,  just  as  wood  varies  in  quali- 
ties when  tested  with  or  across  the  grain.  This  perfect 
regularity  of  structure  in  crystals,  by  which  they  manifest 
different  powers  in  different  directions,  can  only  be  ex- 
plained by  supposing  that  attraction,  in  causing  molecules 
to  cohere  in  crystalline  combination,  does  not  act  equally 
all  around  each  molecule,  but  between  certain  sides  or 
parts  of  one  and  corresponding  parts  of  another ;  so  that, 
when  allowed  to  unite  according  to  their  natural  tenden- 
cies, they  always  assume  a  certain  definite  arrangement. 
This  property  of  molecules  is  called  polarity,  because  in 
these  circumstances  they  seem  to  resemble  magnets^  which 
attract  each  other  by  their  poles. 

72.  Cleavage. — If  we  apply  the  edge  of  a  knife  to  a 
piece  of  mica,  it  may  be  cleft  into  thinner  plates,  and  these 
may  again  be  separated  into  the  thinnest  films.     Nearly  all 
crystals  will  thus  separate  in  certain  directions,  disclosing 
polished  surfaces,  and  showing  the  order  of  formation  of 
successive  parts.     This  mechanical  splitting  of  crystals  is 
termed   cleavage.     Amorphous   solids   do   not  cleave,  but 
fracture  irregularly  and  in  any  direction. 

73.  Derivation  of  Form.— The  cube  (Fig.  27)  may  be 
taken  to  illustrate  change  of  figure,  and  this  is  chiefly  ef- 
fected by  replacing  edges  and  angles  by  planes.     The  cube 
has  twelve  edges  and  eight  solid  angles.     If  plane-surfaces 
are  substituted  for  the  edges,  we  get  the  secondary  form 
(Fig.  28).     If  we  replace  the  solid  angles  by  planes,  we 
have  the  form  Fig.  29.     If  both  these  replacements  occur 
together,    the   more  complex    (Fig.    30)    results.     If  the 


44 


CHEMICAL   PHYSICS. 


edges  of  the  cube  be  replaced  until  all  traces  of  the  original 
planes  disappear  (Fig.  31),  the  rhombic  dodecahedron  is 
formed.  And,  if  the  solid  angles  be  replaced  by  planes  to 
the  same  extent,  we  get  (Fig.  32)  the  regular  octahedron. 


FIG.  27 


FIG.  28. 


FIB.  30. 


FIG.  81. 


Transformations  of  the  Cube. 


We  have  said  that  the  secondary  or  derived  forms  of 
crystals  are  almost  innumerable.  Six  hundred  modifica- 
tions of  the  six-sided  prism  have  been  enumerated  by  Dr. 
Scoresby  among  snow-flakes,  while  M.  Bournon,  in  a  two- 
volume  treatise,  has  delineated  eight  hundred  different 
forms  of  the  mineral  calcite  (calcic  carbonate).  Hauy  has 
described  a  single  crystal  which  had  one  hundred  and 
thirty-four  faces. 

74.  Isomorphism. — When  different  substances  take  upon 
them  the  same  primary  form  or  modifications  of  it,  «they 
are  said  to  be  isomorphous,  and  the  law  which  governs 
their  identification  is  called  isomorphism,  from  the  Greek 
isos,  equal,  and  morphe,  form.  Thus  gold,  silver,  copper, 
alum,  salt,  and  many  other  bodies,  all  crystallize  in  forms 
of  the  monometric  system,  which  perfectly  resemble  each 
other.  Such  perfect  identity  is,  however,  only  met  with  in 
forms  of  this  system  ;  in  all  others,  the  lengths  of  the  axes, 


DIMORPHISM.  45 

or  their  inclinations,  or  both,  varying  slightly,  produce  al- 
ways small  differences  in  the  geometrical  elements  of  their 
forms.  For  this  reason  the  term  homceomorphous,  signify- 
ing similarly  formed,  has  sometimes  been  employed  in 
place  of  the  one  above  mentioned.  Isomorphous  bodies, 
when  crystallizing  from  mixed  solutions,  frequently  remain 
diffused  through  one  another  in  the  solid  state.  Some 
substances  crystallize  in  two  different  forms,  and  are  called 
dimorphous.  Thus,  sulphur  deposited  from  solution  takes 
one  form,  and  when  cooled  from  melting,  another.  Nitre 
crystallizes  in  one  shape  in  large  quantities,  and  takes  an- 
other shape  in  small  quantities.  Substances  crystallizing 
in  three  forms  are  called  trimorphous. 

75.  Molecular  Motions. — The  changes  considered  in  this 
chapter  are  resolvable  into  molecular  movements.  It  is 
held  that  the  molecules  are  always  in  motion,  and  by  vir- 
tue of  their  motions  are  centres  of  molecular  energy.  The 
molecular  units  are  supposed  to  have  three  kinds  of  mo- 
tion. In  solids  they  maintain  their  relative  places,  but 
vibrate  at  such  varying  rates  as  to  emit  all  the  colors  of 
the  spectrum.  In  liquids  the  molecules  are  loosened  from 
their  structural  relations,  and  circulate  among  each  other 
so  rapidly  as  to  give  rise  to  energetic  liquid  diffusion. 
When  the  violence  of  these  motions  is  increased  by  heat, 
the  molecules  are  shot  beyond  cohesive  restraint,  and  as- 
sume the  condition  of  gas.  No  longer  influenced  by  mu- 
tual attractions,  they  are  now  supposed  to  move  with  far 
greater  energy,  flying  about  in  all  directions,  in  extremely 
short,  straight  paths,  striking  and  repelling  each  other,  and 
giving  rise  to  an  expansive  pressure,  known  as  gaseous 
tension.  This  is  the  molecular  explanation  of  the  phe- 
nomena presented  by  the  three  states  of  matter. 


CHAPTER  III. 

II  EAT. 

§1.  Thermal  Expansion. —  Thermometers. 

76.  HEAT  exerts  a  very  powerful  influence  over  the 
states  of  matter,  and  is  so  important  for  the  production 
of  chemical  effects,  that  the  chemist  has  been  called  the 
"  Philosopher  by  Fire."     The  general  science  of  heat  is 
termed   Thermotics,  from   the  Greek  thermos,  hot,  which 
gives  us  also  the  words  thermal,  thermometer,  etc. 

77.  Expansion  of  Solids.— Heat  is  a  force  of  repulsion, 
and  its  general  effect  upon  matter  is  to  separate  its  parti- 
cles, or  to  expand  it.     All  bodies  of  uniform  constitution 
expand  equally  in  all  directions,  when  heated,  while  other 
substances,  as  crystals  and  wood,  in  which  the  particles 
are  differently  arranged  in  different  directions,  expand  un- 
equally.    With   a  given   amount  of  heat,  the  same   sub- 
stance always  expands  to  the  same 

FIG.  33.  degree  ;   but  the  same  quantity  of 

(  '  '  '  'L-J— l^lll '  "-"-^  heat  causes  different  substances  to 
expand  unequally.  This  may  be 
shown  by  riveting  together  thin 

Expanston  of  Compound  Bars.  sliPs  of  different  metals,  for  in- 
stance zinc  and  iron,  into  a  straight 

bar,  Fig.  33.  When  dipped  into  hot  water  it  is  warmed, 
and  the  zinc,  expanding  most,  becomes  longest ;  the  bar 
curves,  the  zinc  forming  the  convex  side.  If  placed  in  ice- 
water,  the  zinc  contracts  most,  and  the  bar  curves  in  the 
opposite  direction.  Heat  thus  antagonizes  cohesion  :  and 


MEASUREMENT   OF   HEAT.  47 

a  quantity  of  heat,  applied  at  a  high  temperature,  produces 
more  expansion  than  the  same  amount  at  a  low  one. 

78.  Expansion  of  Liquids. — If  sufficient  heat  be  imparted 
to  a  solid,  it  overcomes  cohesion,  and  liquefies  it.     Liquids, 
thus  produced  by  heat,  are  also  expanded  by  it,  and  to  a 
much  greater  degree  than   solids.     While  iron  increases 
from  freezing  to  boiling   but  -^  of  its  volume,  water  ex- 
pands ^5,  and  alcohol  £. 

79.  Expansion  of  (rases. — But  liquids  cannot  be  indefinite- 
ly expanded ;  a  sufficient  repulsion  of  their  atoms  changes 
them  into  gases.     As  a  general  law  gases  expand  much 
more  than   liquids,   although    certain    liquids,  as   sulphur 
dioxide,  are  among  the   most  expansible  bodies  known. 
As  there  are  no  varying  cohesions  to  overcome,  gases  ex- 
pand very  nearly  alike,  increasing  from  the  freezing  to  the 
boiling  of  water  more  than  one-third  of  their  bulk. 

80.  Measurement  of  Heat — As  the  effect  of  heat  is  ex- 
pansion, the  measurement  of  expansion  becomes  the  meas- 
urement of  the  force.     The  common  instruments  for  meas- 
uring heat  are  called  thermometers.     They  measure  not 
quantity  of  heat,  but  temperature.     Heat  is  the  force  pro- 
ducing the  effect ;    and   temperature   the   intensity  with 
which  it  acts.     Liquids  are  better  adapted  as  heat-meas- 
urers than  either  solids  or  gases ;  as  in  solids  the  expan- 
sion is  too  slight  to  be  easily  perceptible,  and  gases  are 
too  sensitive  to  changes  of  atmospheric  pressure  to  fit  them 
for  this  purpose. 

81.  Mercurial  Thermometer. — To  make  this  instrument, 
a  fine  glass  tube,  with  a  bulb  upon  the  end,  is  partly  filled 
with  mercury.    The  air  is  expelled  from  the  rest  of  the  tube 
by  heating  it  till  the  mercury  rises  by  expansion  to  the 
top,  and  at  that  moment  the  glass  is  hermetically  sealed 
by  melting  the  end  of  it  with  a  blow-pipe.     As  it  cools, 
the  mercury  falls  in  the  tube,  leaving  a  vacuum  above. 

Mercury  has  several  important  advantages  as  a  ther- 
mometric  fluid.     It  is  readily  obtained  pure,  and  does  not 


48 


CHEMICAL   PHYSICS. 


FIG.  84. 


adhere  to  the  tube  ;  it  is  sensitive  to  heat,  expands  witli 
greater  regularity  than  most  liquids,  and  has  a  range  of 
700°  between  freezing  and  boiling.  Temperatures  below 
the  freezing  point  of  mercury  are  usually  determined  by 
thermometers  filled  with  alcohol,  tinged  with  some  col- 
oring matter,  to  make  it  visible.  As  mercury  boils  at  660°, 
temperatures  above  that  point  are  measured  by  the  expan- 
sion of  the  air,  or  by  the  aid  of  thermo-electric  currents,  the 
metals  iron  and  platinum  being  sometimes  selected  for  the 
combination. 

82,  Thermometric  Scales,— The  sealed  tube  is  attached 
to  a  brass  plate  engraved  with  the  thermometric  scale,  Fig. 
34,  or,  for  chemical  work,  the  divisions  are  en- 
graved directly  on  the  glass  tube.  It  is  then 
dipped  into  ice-water,  and  a  mark  made  oppo- 
site the  top  of  the  column  of  mercury,  called 
the  freezing-point.  It  is  now  introduced  into 
boiling  water,  and  the  height  to  which  the  col- 
umn rises  is  marked  as  the  boiling-point.  These 
are  natural  standard  points  which  serve  as  a 
basis  for  the  division  of  the  scale.  In  the  Cen- 
tigrade thermometer  of  Celsius,  the  freezing- 
point  is  called  zero,  and  the  interval  between 
that  and  the  boiling-point  is  marked  off  into 
100  equal  spaces  called  degrees.  In  Reaumur's 
scale  the  same  space  is  divided  into  80  degrees. 
The  scale  named  after  its  inventor,  Fahren- 
heit, and  which  has,  unfortunately,  come  into 
general  use  in  England  and  this  country,  is 
not  so  simple.  He  divided  the  space  between 
freezing  and  boiling  into  180  degrees ;  but, 
instead  of  starting  at  the  freezing-point,  he 
(^Appendix.)  thought  he  would  find  the  lowest  possible  cold, 
and  make  that  zero.  So  with  snow  and  ice  he  got  the 
mercury  down  to  32°  below  the  freezing-point,  and  com- 
menced counting  there.  On  this  scale,  therefore,  freezing 


•40-B-40 


CONDUCTION  OF  HEAT.  49 

occurs  at  32°,  and  boiling  at  212°.  The  several  scales  are 
distinguished  by  their  initial  letters  F.,  C.,  and  R.  The 
Centigrade,  affording  decimal  subdivisions,  is  the  most 
simple  and  rational,  and  is  gradually  coming  into  use  for 
scientific  purposes.  In  all  of  these  scales,  degrees  belcw 
zero  are  distinguished  from  those  above  by  prefixing  the 
minus-sign  (  — ). 

§  2.    Transference  of  Heat. 

83.  Conduction  of  Heat. — Heat  moves,  or  is  transferred, 
in  several  ways,  known  as  conduction,  convection,  and  ra- 
diation. If  several  marbles  are  stuck  by  wax  to  a  copper 

FIG.  36. 
FIG.  85. 


Conduction  of  Heat  Non-conduction  of  Liquids. 

rod,  Fig.  35,  and  heat  be  applied  to  one  end,  it  gradually 
passes  along  the  rod,  the  wax  is  melted,  and  the  marbles 
drop  off  successively.  The  heat,  in  this  case,  is  said  to  be 
conducted.  Generally,  the  more  dense  a  body  is,  the  better 
it  conducts  ;  solids  are  better  conductors  than  liquids,  and 
liquids  than  gases.  As  a  class,  metals  are  the  best  con- 
ductors, but  they  differ  much  among  themselves  in  this  re- 
spect. The  imperfect  conduction  of  liquids  may  be  shown 
by  filling  a  glass  tube  with  water,  inclining  it  over  a  lamp, 
and  applying  the  flame  at  the  upper  end,  Fig.  36.  The 
water  will  boil  at  the  surface,  while  at  the  bottom  there 
may  still  be  ice  for  a  considerable  time.  Dry  air  is  one  of 
the  poorest  conductors.  Loose  materials,  as  wool,  cotton, 


50  CHEMICAL  PHYSICS. 

sawdust,  are  bad  conductors,  chiefly  owing  to  the  air  in- 
closed in  their  spaces. 

81  Influence  of  Internal  Arrangement. — A  slice  of 
quartz  cut  across  its  axis,  Fig.  37,  was  perforated  with  a 
small  hole  and  covered  with  a  layer  of  white  wax.  A  wire 
was  then  inserted  through  the  orifice  and  heated  by  an 
electric  current.  The  wax  melted  in  an  exact  circle,  which 
showed  equal  conduction  in  all  directions.  A  slice  cut 

FIG.  ST.  FIG.  38. 


Equal  Conduction.  Unequal  Conduction. 

parallel  with  the  axis,  as  in  Fig.  38,  treated  in  the  same 
way,  gave  an  oblong  outline  of  the  melted  wax,  showing 
that  heat  travels  with  more  facility  along  the  crystalline 
axis  than  across  it.  The  metal  bismuth  conducts  both 
heat  and  electricity  better  along  the  planes  of  cleavage 
than  across  them.  The  same  thing  has  been  found  in 
reference  to  wood  ;  it  transmits  heat  better  along  the 
course  of  the  fibres  than  across  them. 

85.  Conduction  influences  Sensation. — The  carpet  feels 
warmer  to  the  naked  feet  than  oil-cloth,  because  the  latter 
conducts  away  the  heat  faster  from  the  skin,  although  both 
are  at  the  same  temperature.     If  the  hand  be  placed  upon 
silver  at  120°,  it  will  be  burned,  owin^  to  the  rapidity  with 
which  heat  leaves  the  metal  and  enters  the  flesh.     Water 
will  not  scald  the  hand  if  it  be  held  quietly  in  it  till  it 
reaches  150°,  while  the  contact  of  air  at  250°  or  300°  may 
be  endured. 

86.  Convection.— Although  liquids  and  gases  are  poor 
conductors,  yet,  from  the  mobility  of  their  particles,  they 
may  be  rapidly  heated  by  a  process  of  circulation  or  con- 


CONVECTION  OF  HEAT.  51 

section.     If  heat  be  applied  to  the  bottom  of  a  vessel  con- 
taining water,  the  lower  portion  of  the  liquid  is  warmed, 
expands,  becomes  lighter,  and  ascends, 
its   place    being    taken    by   the   colder 
liquid  at  the  sides — thus  forming  a  set  of 
currents  which  diffuse  the  heat  through 
the  whole  mass. 

Gases  are  heated  in  the  same  man- 
ner. The  warm  air  in  contact  with  a 
stove  or  other  heated  body  becomes 
lighter,  and  ascends,  while  the  colder 
and  heavier  air  rushes  in  to  supply  its 
place.  This,  becoming  heated,  also  as- 

Circulation  of  Heat 

cends,  and  thus  a  system  of  currents  is 
established,    which    diffuses    warmth    through   the   apart- 
ment. 

87.  Badiation  of  Heat— While  standing  at  some  dis- 
tance from  a  hot  stove  we  are  warmed  by  it.     It  emits  a 
constant  stream  of  heat-rays  in  straight  lines,  at  a  very 
high  velocity,  and  which  have  the  power  of  raising  the 
temperature  of  any  body  that  receives  them.     Heat  moving 
in  this  way  is  called  radiant  heat,  and  the  act  of  transfer- 
ence radiation.     All  bodies  radiate  heat  at  all  times,  the 
rate  of  emission  depending  upon  the  temperature.     If  a 
cannon-ball,  at  1,000°,  be  placed  near  another  at  100°,  they 
radiate  heat  to  each  other,  but  that  at  1,000°  loses  it  faster 
than  it  receives  it,  and  its  temperature  falls ;  while  that 
at  100°  receives  heat  faster  than  it  parts  with  it,  and  its 
temperature   rises.     After  a  time  they  both  come  to  the 
same  temperature,  the  radiations  are  equal,  and  an  equilib- 
rium is  established.     All  bodies  are  thus  exchanging  heat 
with  each  other,  and  tending  to  an  equilibrium  of  temper- 
ature. 

88.  Influence  of  Surface. — Radiation  is  influenced  by 
surface.     A  cubical  vessel  of  tin  had  one  of  its  sides  coated 
with  a  layer  of  gold,  a  second  with  silver,  a  third  with  cop- 


52  CHEMICAL   PHYSICS. 

per,  and  a  fourth  with  varnish.  The  vessel  was  then  filled 
with  hot  water,  and  placed  at  a  little  distance  from  the 
thermometer.  When  the  hot  gold  surface  is  turned  to  it, 
scarcely  a  trace  of  effect  is  observed,  and  so  with  the  cop- 
per and  silver  ;  but,  when  tlie  varnished  surface  is  brought 
round,  a  stream  of  heat  strikes  the  bulb,  and  the  mercury 
quickly  rises.  The  physical  condition  of  the  surface  also 
influences  radiation — rough,  uneven  surfaces  being  more 
active  than  bright  polished  ones ;  hence,  if  the  metal  is 
covered  with  woolen  or  velvet,  its  radiant  power  is  in- 
creased. Bright  metallic  vessels,  therefore,  retain  the 
heat  much  longer  than  those  which  are  tarnished. 

89.  Absorption. — Good  radiators  are  good  absorbers  of 
heat ;  that  is,  the  surfaces  which  can  easily  give  out  heat 
will  easily  take  it  in.     On  the  contrary,  a  bad  radiator,  as 
a  bright  metallic  surface,  is  a  bad  absorber,  and  therefore 
a  good  reflector.     Hence,  the  thinnest  metallic  film  upon 
a  surface  powerfully  protects  it  from  the  action  of  radiant 
heat. 

90.  Dew. — When  the  radiation  of  bodies  is  not  com- 
pensated, their  temperature  sinks.     Such  is  the  case  with 
objects  exposed  to  the  sky  on  clear  nights.     If  good  radia- 
tors, they  rapidly  lose  heat,  and,  cooling  below  the  tem- 
perature of  the  air,  at  length  begin  to  condense  its  moist- 
ure upon  their  surfaces  :  this  is  dew.     The  best  radiators, 
as  grass,  leaves  of  trees,  and  porous  soils,  receive  the  most 
dew,  while  poor  radiators,  as  smooth  stones,  and  hard,  com- 
pact soils,  remain  almost  dry.     Clouds  radiate  back  the 
heat  received  from  the   earth,  so  that  cloudy  nights  are 
warm  and  dewless.     If  the  temperature  sinks  lower  than 
32°,  the  moisture  is  frozen,  and  becomes  frost. 

91.  Two  Kinds  of  Radiant  Heat. — It  is  well  known  that 
radiant  heat  is  constantly  associated  with  light,  and  the 
laws  of  its  movement  are  the  same  as  those  of  light.     That 
which  accompanies  light  is  called  luminous  heat ;  but  that 
which  is  emitted  from  dark  bodies,  as  from  a  stove  below 


RADIATION  OF   HEAT.  53 

redness,  or  from  the  hand,  is  called  obscure,  or  dark  heat. 
But  dark  radiant  heat  obeys  the  same  laws  of  motion  as 
light  and  luminous  heat. 

92.  Diathermancy. — Bodies  which  transmit  heat  freely 
are  called  diathermic,'    those  which  arrest  it,  athermic. 
Rock-salt  (common  salt  in  blocks)  is  the  most  perfect  dia- 
thermic body,  allowing  all  the  heat-rays — those  from  the 
sun  and  the  hand — to  pass  through  with  equal  freedom. 
What  glass  is  to  light,  a  plate 

of  rock-salt  is  to  heat,  and  it  has  FlG- 40- 

hence  been  aptly  termed  "  the 
glass  of  heat."  This  substance 
is  therefore  adapted  to  make 
prisms  and  lenses  for  the  con- 
centration and  dispersion  of 
dark  heat.  If  a  heated  ball 

,  ,         j    ,  ,    ,          f         Glass  intercepting,  and  Rock-Salt 

be  placed  between  a  plate  ot  transmitting  Heat, 

glass  and  one  of  rock-salt,  Fig. 

40,  and  bits  of  phosphorus  be  laid  upon  stands  beyond, 
though  the  salt  be  many  times  thicker  than  the  glass,  the 
dark  heat  passes  freely  through  it,  igniting  the  phos- 
phorus, while  it  is  quite  arrested  by  the  glass. 

93.  Absorption  of  Heat  by  Aqueous  Vapor.— Aqueous 
vapor,  when  condensed   to  minute   particles  of  water,  is 
highly  opaque  to  the  dark  radiations.     Where  the  atmos- 
pheric gases  arrest  one  ray  of  obscure  heat,  the  small  pro- 
portion of  water  suspended  in  the  air  stops  sixty  or  seventy 
rays.     Luminous  solar  heat  penetrates  the  air,  and,  falling 
upon  the  earth,  is  changed  into  obscure  heat,  which  cannot 
be  radiated  back  into  space.     The  watery  particles  are  thus 
the  "  barb  "  of  the  atmosphere  which  prevents  the  escape  of 
the  heat,  and  thus  maintains  the  temperature  of  the  earth. 
It  follows  that,  if  aqueous  vapor  were  withdrawn  from  the 
air,  the   terrestrial  heat  would    so  quickly  radiate  away 
that  the  earth  would  soon  become  uninhabitable ;  the  in- 
visible watery  element  of  the  air  is,  therefore,  the  blanket 


54  CHEMICAL  PHYSICS. 

which  keeps  the  world  warm.  In  all  those  localities  where 
the  atmosphere  is  dry,  the  nightly  loss  of  radiant  heat  is 
great,  so  that  even  in  the  burning  desert  of  Sahara  there 
is  nocturnal  freezing. 

§  3.    Changes  of  Molecular  Aggregation. 

94.  Liquefaction, — Heat   applied   to   solids  overcomes 
their  cohesion  and  changes  them  to  liquids.     That  degree 
of  temperature  which  is  required  to  liquefy  a  substance  is 
called  its  melting-point.     From  hundreds  of  degrees  below 
zero  up  to  thousands  above,  the  various  substances  of  Na- 
ture melt  at  diiferent  temperatures,  showing  that  each  re- 
quires its  particular  amount  of  heat-force  to  throw  it  into 
the  liquid  state. 

95.  Latent  Heat. — In  effecting  this  change,  a  certain 
imount  of  heat  disappears,  or  seems  to  be  used  up  in  the 
process ;  and,  as  it  can  no  longer  be  detected  as  sensible 
heat,  it  is  spoken  of  as  latent  heat.     If  we  take  an  ounce  of 
ice  at  32°,  and  one  of  water  at  174°,  and  put  them  together, 
when  the  ice  is  melted,  we  shall  have  two  ounces  of  water 
at  32°.     The  ounce  of  hot  water  has,  therefore,  lost  142° 
of  its  heat  in  melting  the  ice,  which  amount  is  the  "  latent 
heat "  of  the  resulting  water.     The   amount  of  heat  thus 
consumed  in  altering  the  form  of  bodies,  without  raising 
their  temperatures,  is  different  in  different  cases. 

96.  Specific  Heat. — If  we  expose  equal  weights  of  differ- 
ent substances  to  the  same  source  of  heat,  they  do  not  all 
receive  it  with  equal  readiness  or  in  equal  amounts  ;  some 
will  receive  more  than  others.    Water  requires  thirty  times 
as  much  heat  as  mercury  to  raise  an  equal  weight  of  it 
through  the  same  number  of  degrees.     Hence  bodies  are 
said  to  have  different  capacities  for  heat,  and,  as  each  sub- 
stance seems  to  require  a  particular  quantity  for  itself,  that 
quantity  is  called  its  specific  heat.     The  art  of  measuring 
the  specific  heat  of  bodies  is  called  calorimetry. 


CHANGES   OF  STATE.  55 

97.  Heat  liberated  by  Freezing.— If  the  change  of  a 
solid  to  a  liquid  consumes  force,  the  reverse  change  must 
produce  it  j  the  force  therefore  reappears  as  heat,  upon 
freezing.     As  the  thawing  of  snow  and  ice  in  spring  is  de- 
layed by  the  large  amount  of  heat  that  is  expended  in  the 
forming  of  water,  so  the  freezing  processes  of  autumn  are 
delayed,  and  the  warm   season  -prolonged,  by  the  large 
quantities  of  heat  that  escape  into  the  air,  from  the  chang- 
ing of  water  into  ice. 

98.  Freezing  Mixtures.— Advantage  is  taken  of  the  ab- 
sorption of  heat  in   liquefaction  to  produce  freezing  mix- 
tures, the  most  common  example  of  which  is  salt  and  ice. 
In  this  case  the  salt  melts  the  ice  to  unite  with  its  water, 
which  in  turn  dissolves  the  salt,  so  that  both  solids  are 
changed  to  liquids.     These  changes  require  large  amounts 
of  heat,  which  is  absorbed  from  surrounding  bodies ;  the 
cold  produced  sinking  the  thermometer  40°  below  zero. 

99.  Ebullition. — When  water  is  gradually  heated,  minute 
bubbles  are  formed  at  the  bottom  of  the  vessel,  which  rise 
a  little  way,  are  crushed  in,  and  disappear.     These  consist 
of  vapor  or  steam,  which  is  formed  in  the  hottest  part  of 
the  vessel,  but,  as  they  rise  through  the  colder  water  above, 
are  cooled  and  condensed.    As  the  heating  continues,  these 
rise  higher  and  higher  until  they  reach  the  surface  and 
escape  into  the  air,  producing  that  agitation  of  the  liquid 
which  is  called  boiling  or  ebullition. 

100.  Boiling-Point. — The    temperature   at    which   this 
takes  place  is  called  the  boiling-point,  and  it  varies  with 
different   liquids   and   in    different    circumstances.      It   is 
slightly  influenced  by  the  nature  of  the  containing  vessel. 
To  glass  and  polished  metallic  surfaces  liquids  adhere  with 
greater  force  than  to  rough  surfaces  ;  and,  before  vaporiza- 
tion can  occur,  this  adhesion  must  be  overcome.      Sub- 
stances dissolved  in  a  liquid  also  raise  its  boiling-point  on 
account  of  their  adhesion.     Under  ordinary  circumstances, 
water  boils  at  212°,  but,  saturated  with  common  salt,  its 


56  CHEMICAL  PHYSICS. 

boiling-point  is  224°.  It  has  lately  been  shown  that  the 
amount  of  air  dissolved  in  the  water  affects  its  boiling- 
point,  as  it  presses  the  watery  particles  asunder,  and  thus 
aids  them  to  take  on  the  gaseous  state.  Water  purged 
of  its  air  by  long  ebullition  has  been  heated  to  275°  with- 
out boiling.  When  it  did  boil,  the  water  was  instantly 
changed  into  vapor  with  a  loud  explosion,  the  cohesion  of 
its  particles  being  suddenly  overcome,  like  the  snapping 
of  a  spring,  by  the  repulsive  power  of  the  accumulated 
heat.  But  the  most  important  circumstance  that  influences 
the  boiling-point  is  the  pressure  of  the  atmosphere.  This 
resists  the  rising  vapor,  and,  as  it  fluctuates,  the  boiling- 
point  varies.  The  pressure  becomes  lighter  as  we  ascend 
into  the  atmosphere,  and  the  temperature  of  the  boiling- 
point  is  correspondingly  diminished,  so  that  boiling  water 
is  less  hot  in  high  altitudes  than  in  low  ones. 

101.  The  Spheroidal  State. — Water  adheres  to  most 
surfaces,  but  heat  destroys  this  attraction,  and,  if  drops 
of  it  fall  upon  a  red-hot  plate  of  metal,  they  gather  into 
spheroids,  roll  about,  and  evaporate  very  slowly.  Fig.  41 
represents  a  mass  of  water  in  the  spheroidal  state.  In  this 

FIG.  42. 
FIG.  41. 


Spheroid  of  Water.  Its  Explosion. 

case  the  heat  of  the  metal  produces  a  layer  of  vapor  which 
supports  the  drop,  so  that  it  does  not  touch  the  surface, 
but  is  driven  about  by  currents  of  heated  air.  The  tem- 
perature of  the  spheroid  never  reaches  the  .boiling-point  of 
the  liquid,  as  the  vapor,  being  a  non-conductor,  does  not 
transmit  the  heat  from  the  metal,  and,  besides,  it  is  kep| 


HEAT   IN  EVAPORATION.  57 

cool  by  evaporation  from  its  surface.  If  the  temperature 
of  the  plate  be  allowed  to  fall  to  a  point  at  which  the 
water  wets  its  surface,  it  will  be  suddenly  scattered  in  a 
kind  of  explosive  ebullition,  Fig.  42. 

102.  Vaporization. — The  change  of  solids  or  liquids  by 
the  force  of  heat  to  vapor  is  called  vaporization.     Sub- 
stances which  are  readily  converted  into  vapor  are  said  to 
be  volatile,  while  those  which  are  vaporized  with  difficulty 
are  termed  fixed  or  non-volatile.     The  slow  formation  of 
vapor  from  the  surfaces  of  bodies  is  called  evaporation.    It 
goes  on  at  all  temperatures,  even  from  the  surface  of  ice 
and  snow,  but  is  rapidly  increased  as  the  temperature  rises. 

103.  Heat  of  Vaporization. — A  much  larger  amount  of 
heat  is  spent  in   converting  liquids  into  vapors  than  in 
changing  solids  to  liquids,  while  the  vapors  are  no  hotter 
than  the  liquids  from  which  they  are  formed.     The  heat 
has  been  consumed  in  producing  the  repulsive  motion  and 
the  consequent  enormous  expansion  of  the  gaseous  body. 
If  the  liquid  is  exposed  to  the  air,  it  is  impossible  to  raise 
its  temperature  above  its  natural  boiling-point.     All  the 
heat  added  after  boiling  commences  is  carried  away  by  the 
vapor.     Water  boiling  violently  is  not  a  particle  hotter 
than  that  which  boils  moderately. 

104. — The  quantity  of  heat  which  disappears  during 
evaporation  is  very  large.  With  the  same  intensity  it 
takes  5£  times  as  long  to  evaporate  a  pound  of  water  as  it 
does  to  raise  it  from  freezing  to  boiling ;  it  hence  receives 
5|  times  as  much  heat.  If,  therefore,  180°  were  required 
to  boil  the  pound  of  water,  nearly  1,000°  are  necessary  to 
change  it  to  vapor,  and,  being  spent  in  producing  the 
change  of  state,  it  of  course  disappears  as  sensible  heat. 
This  quantity  is,  therefore,  the  "  latent "  heat  of  steam.  If 
the  process  be  reversed,  and  the  vapor  be  made  to  reas- 
sume  the  liquid  form,  the  heat  reappears.  The  condensa- 
tion of  a  pound  of  steam  will  raise  5^  pounds  of  water 
from  the  freezing  to  the  boiling  point. 


58  CHEMICAL   PHYSICS. 

105.  Cooling  Effects  of  Evaporation.— As  evaporation 
consumes  heat,  it  is  a  cooling  process.     We  experience 
this  in  the  cold  sensation  of  evaporating  a  few  drops  of 
ether  from  the  hand.     As  the  perspiration  evaporates  from 
the  skin,  it  becomes  a  powerful  cooling  agency  and  regu- 
lator of  bodily  temperature,  while  the  vapor  which  escapes 
from  the  breath,  by  its  absorption  of  heat,  exerts  a  cooling 
effect  within  the  body. 

106.  The  Cryophorus,  or  Frost-Bearer,  is  an  instrument 
which  strikingly  illustrates  this  principle.     It  consists  of  a 

tu^)e  w^k  a  glass  bulb  at  eacn  extremity, 
one  of  which  contains  a  little  water.  Air 
is  expelled  from  the  instrument  by  boiling 
the  water,  the  aperture  through  which  the 
steam  escapes  being  sealed,  while  the  re- 
maining space  is  filled  with  vapor.  The 
empty  bulb  is  then  placed  in  a  freezing  mix- 
ture, Fig.  43,  and  the  vapor  condenses,  its 
place  being  supplied  by  vapor  from  the 
water-bulb  above.  Condensation  and  evap- 
oration go  on  so  rapidly  that  the  water  is 

The  Cryophorus.       SOO11  frozen. 

107.  Dew-Point. — The    air   always   contains   moisture, 
the  amount  of  which  varies  with  the  temperature.     The 
power  of  the  air  to  absorb  moisture  is  called  its  capacity 
for  absorption.     When  it  contains  as  much  as  it  is  capa- 
ble of  holding  at   a  given   temperature,  it  is  said  to  be 
saturated,  and  any  lowering  of  the  temperature  condenses 
it  in  the  form  of  clouds,  mist,  fogs,  dew,  etc.     The  degree 
of  temperature  at  which  the  moisture  is  condensed  is  called 
the  dew-point.     If  the  temperature  of  the  air  has  to  fall 
but  a  few  degrees  before  moisture  is  deposited,  the  dew- 
point  is  said  to  be  high,  and  there  is  much  moisture  in  the 
air ;  while,  if  the  temperature  must  fall  far,  the  dew-point 
is  low,  and  the  air  contains  less  moisture.     It  is  obvious, 
therefore,  that,  by  finding  these  two  points  of  tempera- 


ACTION   OF   THE   HYGROMETER. 


59 


FIG.  44. 


ture,  one  can  easily  obtain  the  amount  of  atmospheric 
humidity. 

108.  The  Hygrometer. — This  is  an  instrument  for  meas- 
uring atmospheric  moisture.    Daniell's  hygrometer,  Fig.  44, 
is  constructed  on  the  principle  of  the  cryophorus.    The  long 
limb  ends  in  a  glass  bulb  b  half  filled  with  ether,  into  which 
dips  a  small  thermometer.     The  bulb  a 

on  the  short  limb  is  empty  and  covered 
with  muslin.  The  temperature  of  the 
air  is  shown  by  another  thermometer, 
c,  affixed  to  the  stand  of  the  instru- 
ment. When  an  observation  is  to  be 
made,  a  little  ether  is  poured  upon  the 
muslin,  and,  as  it  evaporates,  the  tem- 
perature of  the  other  bulb  becomes  re- 
duced. When  it  is  sufficiently  cold  to 
condense  the  moisture  of  the  air,  it  will 
be  covered  with  dew.  The  thermome- 
ter in  the  tube  b  shows  at  what  tem- 
perature this  deposition  takes  place, 
and,  of  course,  gives  the  dew-point. 

The  amount  of  moisture  in  the  air  of  our  artificially- 
heated  rooms  is  a  matter  of  great  importance  to  health, 
and  the  hygrometer  is  very  valuable  in  enabling  us  to  de- 
termine it. 

109.  Volume  and  Density  of  Vapor. — Equal  bulks  of  dif- 
ferent liquids  generate  unequal  volumes  of  vapor.     Water 
yields  a  larger  amount  than  any  other  liquid.     While  a 
cubic  inch  of  water  gives  1,694  inches  of  vapor,  a  cubic 
inch  of  alcohol  yields  528,  one  of  ether  298,  and  of  oil  of 
turpentine  193.     But,  the  less  the  volume  of  vapor,  of 
course  the  greater  its  density.      The  density  of  vapor  is 
increased,  either  by  cold  or  pressure.     The  point  at  which 
its  temperature  cannot  be  further  lowered,  without  return- 
ing to  the  liquid  state,  is  called  its  maximum  density. 

110.  Elastic  Force  of  Vapors. — All  vapors  are  elastic, 


DauielPs  Hygrometer. 


60 


CHEMICAL  PHYSICS. 


FIG.  J5. 


and  have  a  tendency  to  diffuse  themselves  through  space, 
exerting  more  or  less  force  against  any  obstacle  that  re- 
sists their  expansion.  This  expansive  force  of  vapors  is 
called  their  elastic  force  or  tension.  The  expansive  force 
of  heat,  acting  through  the  vapor  of  water,  is  the  impelling 
power  of  the  steam-engine. 

111.  Distillation  consists  in  vaporizing  a  liquid  by  heat 
in  one  vessel,  and  condensing  it  by  cold  in  another,  Fig. 

45.  The  object  may  be  either 
to  separate  a  liquid  from  non- 
volatile substances  dissolved  in 
it,  as  in  distilling  water,  to  purify 
it  from  foreign  ingredients,  or  to 
separate  two  liquids  which  evap- 
orate at  different  temperatures, 
as  alcohol  and  Avater.  In  the 
latter  case,  the  heat  is  carried 
just  high  enough  to  vaporize  the 
most  volatile  liquid.  The  product 
of  the  process  is  called  the  distil- 
late. When  solids  are  vaporized,  the  process  is  termed 
sublimation,  and  the  condensed  vapor  a  sublimate. 

112.  Condensation  of  Gases. — When  a   gas   loses  heat 
enough  to  change  it  to  the  liquid  or  solid  state,  it  is  said  to 

be  condensed.  Under  the  joint  effect  of 
pressure  and  extreme  cold,  many  gases 
once  considered  permanent  have  been  re- 
duced to  liquids,  and  some  even  to  the  solid 
condition.  Dr.  Faraday  effected  this  by 
a  very  simple  method.  He  placed  the  ma- 
terials from  which  the  gas  was  to  be  gen- 
erated in  one  end  of  a  glass  tube  bent  in  the  middle,  which 
was  then  hermetically  sealed,  Fig.  46.  The  expanding  gas 
confined  in  so  small  a  space  exerted  a  tremendous  pressure, 
the  force  of  which  condensed  a  portion  of  it  into  a  liquid 
in  the  other  end  of  the  tube,  which  was  immersed  in  a 


Distillation. 


FIG.  46. 


Condensation  Tube. 


CHEMICAL  INFLUENCE  OF  HEAT  61 

freezing  mixture  to  facilitate  the  process.  By  this  method, 
and  at  a  temperature  of  —166°,  he  succeeded  in  liquefying 
carbonic  dioxide,  chlorine,  ammonia,  and  several  other  gases, 
More  recently  M.  Natterer,  of  Vienna,  applied  a  cold  of 
—220°  F.,  and  a  pressure  of  3,000  atmospheres ;  but  some 
of  the  gases,  as  oxygen,  hydrogen,  nitrogen,  refused  to 
liquefy,  even  under  this  tremendous  force. 

113.  Heat  and  Chemical  Action. — Besides  these  physi- 
cal changes  and  transformations,  heat  is  also  employed  to 
effect  innumerable  chemical  changes.  By  means  of  lamps, 
baths,  and  furnaces,  the  chemist  is  able  to  subject  bodies 
to  all  degrees  of  temperature,  and  to  promote  and  modify 
their  action  on  each  other.  By  its  repellant  action  upon 
the  constituent  parts  of  matter,  heat  overcomes  chemical 
attraction,  destroys  compounds,  and  brings  new  affinities 
into  play  with  the  production  of  new  substances.  At  a 
sufficiently  high  temperature,  indeed,  we  can  conceive  the 
repulsion  to  be  so  great  that  all  affinities  are  suspended, 
and  the  chemical  elements  are  dissociated. 


§  4.    The  Nature  of  Heat. 

114.  Heat  and  Cold. — The  difference  between  heat  and 
cold  is  merely  one  of  degree,  and  we  must  be  careful  not 
to  misinterpret  their  impressions  upon  ourselves.  If  we 
plunge  one  hand  in  ice-water  and  the  other  in  hot  water, 
and  then  transfer  both  to  water  intermediately  warm,  it 
will  seem  hot  to  the  one  and  cold  to  the  other.  Indeed, 
if  we  trusted  our  ordinary  sensations,  we  should  believe  in 
two  opposite  principles  of  heat  and  cold,  a  doctrine  which 
was  long  advocated  until  it  was  found  that  these  are  mere- 
ly relative,  and  that  cold  is  but  the  absence  of  heat.  In- 
tense heat  and  intense  cold  produce  the  same  sensations ; 
fro/en  mercury  blisters  the  flesh  like  hot  iron.  Putting 
aside,  then,  our  sensations,  what  is  it  that  we  know  con- 
cerning the  n:iture  of  heat  ? 


62  CHEMICAL  PHYSICS. 

115.  The  Caloric  Hypothesis. — In  the  foregoing  brief 
statement  of  the  actions  and  effects  of  heat,  we  have  con- 
fined ourselves  to  facts  which  can   be  shown  by  experi- 
ment, and  have  spoken  of  heat  merely  as  a  force,  or  agent. 
But  how  are  its  effects  produced  ?     It  has  long  been  re- 
garded as  a  kind  of  matter — a  subtile  fluid — an  imponder- 
able element,  whose  entrance  into   our   bodies  produces 
warmth,  and  its  escape  cold.     This  fluid  caloric  was  sup- 
posed to  be  stored  up  in  the  interstices  of  bodies,  some 
holding  more  than  others,  according  to  their  various  capaci- 
ties.    It  was  assumed  to  have  an  attraction  for  the  parti- 
cles of  matter,  and  to  combine  with  them,  while  its  own 
particles  are  self-repulsive,  and  thus  cause  the  atoms  with 
which  they  unite  to  repel  each  other.     This  notion  of  the 
materiality  of  heat  is   now    generally    abandoned   in   the 
scientific  world. 

116.  Grounds  of  a  New  Theory. — Facts  were  pointed 
out  in  the  last  century  by  Count  Rumford   which  were 
wholly  inconsistent  with  the  caloric  hypothesis>  and  many 
other  facts  of  similar  import  have  been   since  observed. 
If  an  iron  bar  is  struck  upon  an  anvil,  its   temperature  is 
raised,  and,  if  it  continues  to   be  hammered,  it  may  be 
made  red  hot.     Two  sticks   may  be  rubbed   together  till 
they  take  fire  ;  and  water  may  be  agitated  by  friction  till 
it  boils.     It  is  a  general  law,  that  arrested  mechanical  mo- 
tion produces  heat,  and  that  the  amount  of  heat  produced 
depends  not  at  all  upon  the   capacities  of  bodies  for  heat, 
but  upon  the  amount  of  mechanical  force  expended.     Prof. 
Rood  made   the  following   beautiful  experiment :   A  ball 
weighing  a  pound  is  allowed  to  fall  from  a  height  of  one 
or  two  inches  on  a  thermo-electric  couple  made  by  solder- 
ing together  German-silver  and  iron.     The  heat  thus  de- 
veloped generates  a  current  of  electricity  which  is  meas- 
ured by  a  galvanometer.     The  amount  of  heat  generated 
was   found   to   be    directly  proportional   to   the   distance 
through  which  the  ball  fell.     It  has  been  demonstrated 


THE   LATER   VIEWS   OF   HEAT.  63 

that  772  pounds  falling  through  one  foot  of  space  pro- 
duces sufficient  heat  to  raise  one  pound  of  water  1°  F. ; 
and  it  has  been  further  proved  that  one  pound  of  water 
falling  through  one  degree  of  temperature  gives  out  suffi- 
cient heat  to  raise  772  pounds  one  foot  high.  This  is 
known  as  the  mechanical  equivalent  of  heat,  and  was  estab- 
lished by  Dr.  J.  P.  Joule,  of  Manchester,  England,  in  1850. 

117.  Heat  as  a  Mode  of  Motion. — It  is,  therefore,  now 
held  that  heat  and  mechanical  force  are  convertible  into 
each  other,  and  this  puts  an  end  to  the  conceptions  of  heat 
as  a  material  fluid  ;  for,  to  be  interchangeable,  their  forces 
must  have  a  common  nature.  The  convertibility  is  between 
molar  motions  and  molecular  motions — the  motion  of 
masses  and  the  motion  of  particles.  When  a  body  is 
struck,  the  mechanical  motion  is  arrested,  but  there  is  no 
destruction  of  force  ;  it  is  only  communicated  to  the  parti- 
cles of  the  body  which  are  thrown  into  internal  motion, 
and  this  is  manifested  as  heat.  Heat  is,  therefore,  now 
defined  as  a  "  mode  of  motion "  among  the  constituent 
parts  of  matter.  We  say  that  bodies  are  heated  and 
cooled,  and  that  one  warms  another  near  it.  But  we 
strictly  mean  only  that  they  expand  and  contract,  and 
that  a  body  in  expanding  contracts  others,  and  in  contract- 
ing expands  them.  Hence,  we  find  the  effect  of  heat  to  be 
simply  a  motion  of  expansion  in  matter  communicable 
from  body  to  body.  The  motion  of  a  mass  implies  the 
motion  of  its  parts.  If  a  body  expands,  it  is  because  its 
parts  have  receded  farther  from  each  other,  that  is,  have 
moved.  Heat  is  therefore  such  a  motion  among  the  mole- 
cules of  a  body  as  gives  rise  to  expansion. 

The  later  views  of  the  relations  of  force  all  favor  the 
idea  that  the  minute  molecules  of  matter  are  in  a  state 
of  incessant  movement.  As  nothing  around  us  is  at  rest, 
the  idea  of  the  quiescence  of  the  internal  parts  of  matter 
would  seem  to  contradict  the  whole  course  of  Nature. 
Tlie  celestial  bodies  are  in  perpetual  oiderly  movement, 


64  CHEMICAL   PHYSIC -. 

and  it  seems  highly  probable  that  at  the  other  extreme  of 
being  there  is  also  an  order  of  motions  equally  regular  and 
systematic. 

118. — As  heat  is  a  molecular  motion,  intensity  of  this 
motion  determines  temperature.  When  a  body  is  heated, 
the  vibration  of  its  molecules  is  augmented  ;  the  particles 
move  through  larger  spaces ;  are  urged  apart,  and  thus 
cause  the  body  to  expand  in  bulk.  When  the  vibrations 
of  the  particles  of  solids  become  sufficiently  violent,  they 
are  loosened  from  the  cohesion,  and,  continuing  to  oscillate 
as  before,  they  are  now  at  liberty  to  slip  or  flow  around 
and  among  each  other.  This  is  the  liquid  state,  in  which 
rigidity  has  disappeared.  A  further  augmentation  of  heat 
increases  the  swing  of  the  molecules  until  they  are  thrown 
quite  beyond  the  sphere  of  cohesion,  and  fly  asunder  into 
the  vaporous  or  gaseous  state. 

119.  The  Railway-Train. — In   this   case  the  heat  of 
combustion  is  spent  in  communicating  to  water  the  molec- 
ular vibration,  which  changes  it  to  steam,  and  this  molecu- 
lar motion  is  then  converted  into  the  mechanical   move- 
ment of  the  piston  and  the  flight  of  the  train.     Wrhen  the 
train  is  to  be  stepped  the   breaks  are   applied,  heat  and 
sparks  are  produced,  and  the   motion  of  the  cars  is  con- 
densed back  again  into  the  molecular  vibrations  of  heat. 
This  explanation  of  the  nature  of  heat  is  known  as  the 
dynamical  theory. 

120.  Heat  of  Combustion,— The  chief  source  of  artificial 
heat  is  combustion.     Combustion  is  that  particular  form  of 
chemical  action   which  takes  place  when  the   simple  ele- 
ments of  which  certain  substances,  as  wood,  coal,  fats,  il- 
luminating gas,  etc.,  are  composed,  enter  into  new  combi- 
nations with  oxygen,  one  of  the  constituents  of  our  atmos- 
phere, or  any  other  gaseous  body,  with  so  much  energy  as 
to  involve  the  conversion  of  the  excess  of  chemical  force, 
brought  into  play,  into  other  modes  of  motion,  chief  among 
which  are  heat  and  light. 


CHAPTER  IV. 

ELE  CTRICITY. 

§  1.  Frictional  Electricity. 

121.  Electrical  Excitation. — If  a  dry,  warm  glass  tube 
be  rubbed   with  a   silk   handkerchief,   a  feeble,  crackling 
noise  is  heard ;  and,  if  it  be  dark,  faint  sparks  will  appear 
to  dart  from  the  surface  of  the  glass.     If  the  tube  be  now 
presented  to  any  light   substances,   as  bits  of  paper  or 
feathers,  they  are  attracted  to  the  glass.     The  force  or 
affection  of  matter  thus  made  active  is  called  electricity. 
Bodies  in  which  it  is  displayed  are  said  to  be  electrically 
excited  or  electrified,  and  are  termed  electrics.     They  are 
numerous,  including  all  resinous,  gummy,  and  glassy  sub- 
stances, hair,  silk,  dry  gases,  and  air. 

122.  Conductors  and  Insulators. — Some  bodies,  as  the 
metals,  water,  charcoal,  etc.,  allow  electricity  to  pass  read- 
ily through  them,  and  are  hence  called  conductors.     Other 
substances,  such  as  glass,  resins,  wool,  do  not  readily  allow 
its  passage,  and  are  termed  non-conductors.     As  the  latter 
tend  to  arrest  or  confine  electricity,  they  are  called  insu- 
lators.    Air  is  a  non-conductor,  and  acts  as  a  universal  in- 
sulator.    All  electrical  manifestations  around  us  depend 
upon  this,  for,  if  air  were  a  good  conductor,  no  body  could 
preserve  its  electricity.     Yet  moisture  conducts,  so  that 
the  air,  when  charged  with  dampness,  carries  off  electricity 
quite  rapidly.     For  successful  experiments,  therefore,  the 
air  must  be  dry. 


66 


CHEMICAL  PHYSICS. 


123.  Two  Electricities. — There  are  two  kinds  of  elec- 
tricity ;  that  from  glass  is  called  vitreous,  and  that  from 
wax  resinous.     Each  is  self-repulsive,  but  bodies  excited 
both  ways  attract  each  other ;  or,  as  it  is  commonly  ex- 
pressed, like  electricities  repel,  and  unlike  attract.     Frank- 
lin held  that  bodies  vitreously  electrified  have  an  excess 
of  it  above  their  natural  share,  which  excess  he  called  the 
positive  state;  while  bodies  resinously  electrified  are  de- 
ficient in  the  fluid,  or  in  a  negative  condition.     The  posi- 
tive electrical  state  he  distinguished  by  the  plus  sign  (  +  ), 
and  the  negative  by  the  minus  sign  (— ).     Positive  elec- 
tricity is,  however,  no  more  positive,  real,  or  powerful  than 
negative,  and  the  terms  might  be  reversed  so  far  as  the 
character  of  the  electricities  is  concerned. 

124.  Electric  Tension. — The  electrical  excitement  of  a 
body  may  rise  so  high  as  to  overcome  the  resistance  which 
confines  it   and   escape,  rending   a   passage   through  the 
air,  when  all  excitement  disappears.     A  body  electrically 
excited  is  said  to  be  charged ;  the  restoration  of  equilib- 
rium is  called  discharge,  and  is  seen  in  the  electric  spark 

and  the  flash  of  lightning.  The 
degree  of  excitement  or  intensity 
of  the  charge  is  called  electrical 
tension,  and  may  be  compared  to 
the  pressure  of  steam,  or  the  bend- 
ing of  a  bow  or  spring ;  its  dis- 
charge, to  their  release. 

125.  Electrical  Induction.— Elec- 
trical bodies  act  at  a  distance  to 
disturb  the  equilibrium  of  neigh- 
boring bodies.  If  an  excited  glass 
rod  be  brought  near  an  electro- 
scope, though  there  be  no  con- 
tact, the  gold  leaves  suspended  in 
the  jar  below  will  diverge,  Fig.  47,  and,  upon  examination, 
it  will  be  found  that  the  cap  is  negatively  electrified,  and 


FIG.  47. 


Induced  Electricity. 


POLAR  STATES  OF   MOLECULES.  67 

the  leaves  positively.  The  approach  of  the  excited  tube 
decomposes  their  natural  electricity,  the  negative  element 
being  attracted,  and  the  positive  repelled.  This  action  of 
an  excited  body,  without  discharge,  through  a  medium 
upon  distant  bodies,  is  known  as  electrical  induction. 

Induction  is  a  kind  of  preparation  for  discharge.  When 
electricity  is  about  to  move,  or  discharge  to  occur,  the 
whole  course  through  which  it  will  pass  is,  as  it  were,  felt 
out  beforehand  ;  at  first  and  infallibly  the  line  of  least  re- 
sistance is  found  and  pursued.  If  two  conductors  are  be- 
fore it,  it  takes  the  easiest  course  at  the  outset. 

126.  Course  of  the  Discharge. — Fig.  48  represents  frag- 
ments of  gold  leaves  casually  laid  upon  paper,  and  produ- 
cing with  the  paper  a  series  of  bad  and  good 
conductors.     A  discharge  finds  its  path  across       FlG-  48< 
the  interrupted  circuit  from  P  to  j\^  burning 

up  the  leaves  and  parts  of  leaves,  as  shown  by  H  n 

the  shaded  track.     These  remarkable  results  •  </> 

are  necessary  consequences  of  the  principle 
of  induction.     The  charged  body  induces  at- 
tractions  in  all  directions,  and  the  discharge      • 
will,  of  course,  be  determined  through  that         %. 
range  of  materials  which,  from  their  nature        — ^ 
and  position,  are  most  excited  ;  which  present        ** 
the  strongest  attractions,  and,  of  course,  the 
least  obstruction.  H 

127.  Theory  of  Induction.— As  there  are 

all  degrees  of  conduction  and  insulation,  Dr.  N 
Faraday  held  that  we  must  look  upon  con- 
duction  and  induction  as  only  different  de- 
grees of  the  same  mode  of  movement ;  in  all  cases,  it  is 
an  effect  communicated  through  molecules.  If,  when  a 
body  is  electrified,  its  particles  discharge  instantaneously 
into  each  other,  conduction  is  the  consequence.  If  the 
molecules  do  not  readily  discharge,  but  hinder  the  course  of 
the  electricity,  they  are  immediately  forced  into  positions 


68  CHEMICAL   PHYSICS. 

of  constraint :  they  become  polarized,  their  opposite  sides 
having  opposite  properties,  and,  as  each  particle  induces  a 
state  of  polar  tension  in  its  neighbor,  the  effect  is  trans- 
ferred to  a  distance.     In  Fig1.  49,  P  represents  a 

FIG.  49. 

•  positively  charged  body,  and  abed  intermedi- 
ate particles  of  air.  These  are  thrown  into  op- 
posite states  or  polarized,  as  is  represented  by 

the  white  and   black   sides  of  the  spheres,  and 
Q  Q  Q  $ 

thus  the   effect  is   propagated  to  the  body  JVJ 

„  ,    which   is    electrically   excited.      We   have   said 
that   insulators    arrest    electricity,  but    en    this 
view  they  only  stop  movement  by  conduction ; 
they  transmit  it  by  induction  through  the  polari- 
of  Atoms"    zation  of  their  particles.     As  the  polar  particles 
are  in  active  relations  of  force  to  those  around,  it 
is  obvious  that  the  effects  may  be  propagated  in  various 
directions.     Hence  the  polarization  may  occur  in  curved 
lines,  and  induction  take  place  round  corners  and  behind 
obstacles. 

§  2.    Magnetism. 

128.  Natural  and  Artificial  Magnets.— If  a  fragment 
of  iron-ore  called  the  loadstone  is  suspended,  it  turns  one 
of  its  sides  to  the  north,  and  the  opposite  to  the  south ;  it 
attracts  to  itsslf  particles  of  iron  or  steel,  and  is  called  a 
natural  magnet.     If  a  steel  bar  be  rubbed   by  a  natural 

magnet,  it  acquires  magnetic  prop- 
erties, and  becomes  an  artificial 
magnet.  If  properly  shaped  and 
poised  upon  a  pivot,  Fig.  50,  it 
takes  a  northerly  and  southerly 
direction.  The  extremity  which 
Magnetic  Needle.  points  northward  is  called  the 

north   pole   of    the    magnet,    and 
that  which  turns  southward,  the  south  pole. 

129.  Polarity. — If  a  second  needle  be  brought  near  the 
first,  it  will  be  noticed  that  they  exert  a  powerful  influence 


INDUCED   MAGNETISM. 


FIG.  51. 


over  each  other.  The  north  pole  of  each  attracts  the  south 
pole  of  the  other,  while  north  pole  repels  north  pole,  and 
south  pole  repels  south  pole.  In  short,  like  poles  repel, 
and  unlike  attract  each  other.  These  influences  are  ex- 
erted through  all  kinds  of  matter — glass,  wood,  metals, 
or  the  human  body — and  through  a  vacuum.  The  magnetic 
force  is  manifested  chiefly 
at  the  poles.  If  a  sheet  of 
paper  be  laid  upon  a  mag- 
netic bar,  and  iron  filings 
be  dusted  over  it,  on  gen- 
tly tapping  the  paper,  they 
gather  thickly  around  the 
poles,  extending  away  in  Magnetic  Curves. 

curved    lines,  called    mag- 
netic curves,  Fig.  51.     Thus  the  two  magnetic  forces  are 
always  produced  simultaneously ;  are  equal  in  amount,  but 
opposite  in  direction ;  and  as  these  opposite  powers  are 
manifested  in  the  poles  of  the   magnet,  they  are  called 
polar  forces,  while  the  property  excited  is  termed  polarity. 
130.  Magnetic  Induction. — The  preceding  experiments 
show  that  the  magnet  has  the  power  of  exciting  magnet- 
ism in  adjoining  bodies ;  P,fl  53 
in  fact,  each  of  the  little 
particles  of  iron  becomes 
a  magnet  with   a  north 
and   south   pole.      This 
may  be  proved   by  pla- 
cing several  bars  of  soft 
iron  around  the  pole  of 
a  magnetic  bar,  Fig.  52, 
when   they   all    become 
temporarily      magnetic. 
The  permanent   magnet 
induces  the  influence  in    Ma^netic  ™ucttan. 


FIG.  52. 


Magnetic  Chain. 


the  adjacent  bars,  which  are  hen  33  said  to  be  magnetized 


70 


CHEMICAL   PHYSICS. 


FIG.  54. 


IS       NiiS     NjJS 

A  Broken  Magnet. 


by  induction.  A  key  may  be  suspended  by  a  magnet, 
Fig.  53,  and  this  will  hold  a  second  smaller  key,  this 
a  nail,  and  the  nail  a  tack,  all  receiving  their  magnet- 
ism by  induction  from  the  bar,  and  each  possessing  its 
separate  north  and  south  polarity. 

131.  Polarity  of  Particles. — Now,  the  particles  of  the 
magnet  are  in  the  same   condition  as  the  magnet  itself. 
If  a  magnet  is  broken,  as  in  Fig.   54,  and  the  pieces  are 

broken  again  and  again,  the  small- 
est particles  still  have  opposite 
poles.  Each  particle  acquires  po- 
larity, and  acts  by  induction  upon 
all  the  others,  the  opposite  pow- 
ers becoming  accumulated  at  the  opposite  extremities  of 
the  bar.  It  may  be  observed  that  while  steel  retains  its 
magnetism — that  is,  its  particles  remain  fixed  in  their  polar 
relation — soft  iron,  on  the  contrary,  only  remains  a  magnet 
while  immediately  acted  upon. 

132.  Diamagnetism. — Magnetic  bars  are  usually  bent  in 
the  shape  of  a  horseshoe,  and  their  poles  are   connected 
by  a  piece  of  iron  called  an  armature.     The  space  between 

the  poles  is  called  the  mag- 
netic field /  a  line  joining  the 
poles  the  axis ;  the  line  at 
right  angles  with  this,  the 
equator.  All  substances  which, 
when  freely  suspended  between 
the  poles,  of  a  magnet,  arrange 
themselves  axially,  are  classed 
as  magnetic.  Iron,  nickel,  co- 
balt, and  oxygen,  are  the  most 
important.  Certain  bodies, 
when  suspended  in  the  mag- 
netic field,  assume  an  equa- 
torial direction,  as  if  repelled 
by  the  poles,  and  these  are  said  to  be  diamagnetic.  In 


FIG.  55. 


Diamagnetism. 


CUR  KENT   ELECTRICITY.  71 

Fig.  55,  b  represents  a  bar  of  diamagnetic  bismuth  sus- 
pended by  fibres  of  unspun  silk  between  the  two  poles  of 
a  magnet.  This  property  is  also  manifested  by  antimony, 
wood,  leather,  water,  etc.  ;  in  fact,  all  substances  not  mag- 
netic are  now  regarded  as  diamagnetic. 

§  3.     Voltaic  Electricity. 

133.  The  Voltaic  Circuit. — We  are  now  to  consider 
electricity  in  a  form  more  closely  related  to  chemical 
action.  Tt  was  first  discovered  by  Galvani,  and  has  been 
called  after  him  galvanism  ;  but  its  most  illustrious  culti- 
vator was  Volta,  from  whom  it  is  also  called  voltaic  elec- 
tricity. A  strip  of  zinc  and  one  of  copper  are  placed  in  a 
vessel  containing  water,  to  which  has  been  added  a  little 
sulphuric  acid.  If  not  permitted  to  touch  each  other,  as  in 
Fig.  56,  there  is  no  effect.  But,  if  brought  into  contact,  as 
seen  in  Fig.  57,  several  results  ensue.  The  acid  in  the 
water  grows  weaker ;  the  zinc  strip  is  corroded,  and  bub- 

F,o.  K 


No  Effect.  The  Voltaic  Circuit. 

bles  of  gas  are  seen  to  escape  from  the  surface  of  the  copper. 
If  the  metals  are  separated,  the  action  ceases ;  and,  if  this 
is  done  in  the  dark,  a  minute  spark  will  be  seen.  Electrici- 
ty seems  to  flow  round  and  round  in  the  direction  of  the 
arrows,  like  an  invisible  stream.  The  combination  through 
which  it  passes  is  termed  a  voltaic  circuit,  and  the  circulat- 
ing force  an  electric  or  electromotive  current.  The  electric 
current  originates  in  chemical  changes,  and  requires  a  com- 
pound liquid  capable  of  decomposition  by  one  of  the  metals. 
4 


72  CHEMICAL  PHYSICS. 

The  source  of  the  electricity,  in  this  case,  is  the  decom- 
position of  the  sulphuric  acid  forming  zinc  sulphate,  and  set- 
tiug  free  hydrogen  gas.  The  zinc  sulphate  being  dissolved 
in  the  liquid,  the  plate  is  kept  clean  and  the  action  main- 
tained, till  the  metal  is  consumed,  or  the  acid  all  neutralized. 

134.  Electrodes.— To  the  plates  are  often  soldered  wires 
with  terminals  of  platinum  to  withstand  the  action  of  cor- 
rosive liquids.     The  ends  of  these  wires  are  known  as  the 
poles  of  the  circuit,  from  an  idea  that  they  exerted  an  at- 
tractive and  repellant  action,  like  the  poles  of  a  magnet. 
But  Faraday  has  proved  that  there  is  no  attraction  or  re- 
pulsion in  the  case,  and  suggested  the  better  term  elec- 
trodes^ which  means   simply  a  door  or  way  for  the  elec- 
tricity.    The  copper  pole  is  termed  positive,  and  the  zinc 
pole  negative.     Whatever  be  the  metals  used,  that  which 
is  chemically  acted  upon  and  originates  the  electricity  is 
termed  positive. 

135.  The  Voltaic  File. — The  power  of  the  circuit  may 
be  increased  by  repeating  its  elements.     The  pile  discov- 
ered  by  Volta  and  named  after  him   was  the  first  con- 
trivance for  ausrmenting1  the  force  of  the  elec- 

FIG.  58. 

trie  current.     It  is  made  by  preparing  small 
plates  or  disks  of  metal,  usually  copper  and 
zinc,  and  placing  between  them  pieces  of  flan- 
nel moistened  with  an  acid  or  saline  soluiion. 
>c    Such  a  pile  is   represented  in   Fig.  58.     The 
cloth  is  placed  between  the  metals,  and  the 
order  begun    is    preserved.      Commencing  at 
the  bottom  there   is  copper   (c),  flannel   (/"), 
zinc  (2),  and  upon  that  copper,  flannel,  zinc, 
Voltaic  Pile,     and  so  on  to  fifty  or  a  hundred  sets,  as  may  be 
desired  (Fig.  58).     The  lower  or  copper  end  is 
positive,  and  the  other  negative ;  a  current,  therefore,  moves 
in  the  direction  of  the  arrows.      This  form  of  instrument 
gives  a  strong  effect  at  first,  but  rapidly  declines  in  power. 

136.  The  Galvanic  Battery. — To  augment  the  electrical 


ELECTRICAL   BATTERIES. 


73 


FIG.  50. 


Voltaic  Battery. 


FIG.  60. 


effect,  and  at  the  same  time  secure  steadiness  of  action  and 
convenience  of  management, 
the  compound  circuits  are  ar- 
ranged in  other  forms  known 
as  voltaic  or  galvanic  batter- 
ies. A  series  of  vessels,  called 
cells,  containing  an  acidulated 
liquid,  is  arranged,  in  each 
of  which  there  is  a  plate  of 
copper  and  another  of  zinc ;  the  copper  plate  of  one  cell 
being  connected  by  a  copper  wire  with  the  zinc  plate  of 
the  preceding  cell,  Fig.  59. 

137.  Daniell's  Battery. — Prof.  Daniell  made  an  impor- 
tant improvement  in  the  battery  by  using  two  different 
fluids  separated  by  a  porous  partition. 
Fig.  60  exhibits  a  section  of  Darnell's 
cell :  a  is  an  outer  cylinder  of  copper 
rilled  with  b,  an  acid  solution  of  blue 
vitriol,  which  is  kept  saturated  by  crys- 
tals resting  upon  the  perforated  shelf 
/;  c  is  a  tube  of  porous  ware,  or  un- 
oiled  leather,  filled  with  tf,  1  part  of  sul- 
phuric acid  to  7  of  water,  and  into  this 
is  plunged  a  rod  of  amalgamated  zinc  e. 
To  the  copper  and  zinc  are  attached 
binding  screws  for  wire  connections. 
When  the  action  commences,  a  double  set  of  changes 
rakes  place  in  the  liquid.  Oxide  of  zinc  is  formed  in  the 
inner  vessel,  and  the  polarizing  action  taking  place  through 
the  porous  wetted  body  c,  the  sulphate  of  copper  is  decom- 
posed in  the  outer  vessel.  The  sulphuric  acid  set  free  is 
gradually  transferred  to  the  inner  vessel,  while  the  hydro- 
gen, instead  of  being  set  free,  combines  with  the  oxygen 
of  the  oxide  of  copper,  precipitating  metallic  copper  upon 
the  surface  of  the  outer  cylinder.  A  variety  of  improved 
batteries,  such  as  Grove's  and  Bunserfs,  are  now  in  use. 


Danieirs  CelL 


74  CHEMICAL  PHYSICS. 

138.  Quantity  and  Intensity. — In  the  battery  the  quan- 
tity of  electricity  depends  upon  the  size  of  the  plates  ;  the 
intensity,  upon  the  number  of  them.     If  we  increase  the 
size  of  a  pair  of  zinc  and  copper  plates,  we  increase  the 
quantity  of  the  electricity  they  produce,  but  not  its  inten- 

sit}- ;  while,  if  we  reduce 
FlG-  61-  the    size,    we   reduce    the 

quantity,  the  intensity  re- 
maining the  same.  On 
the  contrary,  if  we  multi- 
ply the  number  of  pairs 
of  equal  size,  the  inten- 
sity is  augmented  at  an 

Accumulating  Intensity.  •> 

equal  rate,  while  the  quan- 
tity is  unchanged.  The  electricity  developed  by  a  single 
pair  is  exceedingly  feeble ;  the  second  cell  adds  no  more 
to  it,  but  intensifies  its  power.  In  Fig.  61  the  arrows  illus- 
trate the  accumulating  intensity. 

139.  Induced  Currents. — If  two  conductors  are  placed 
near  and  parallel  to  each  other,  a  current  sent  through  one 
induces  an  opposite  current  in  the  second.     At  the  mo- 
ment the  circuit  is  formed  and  the  primary  current  passes, 
a  secondary  current  is  produced   in  the  opposite  direction 
in  the  second  wire.     If  one  or  two  hundred  feet  of  stout 
copper  wire  are  wound  into  a  close  coil,  and  then  twenty 
or  thirty  thousand  feet  of  much  finer  wire  (both  well  cov- 
ered with  silk)  be  wound  into  a  secondary  coil  around  the 
first,  a  current  sent  through  the  inner  wire,  and  rapidly  in- 
terrupted, induces  very  powerful  currents  in  the  outer  coil, 
which  give  rise  to  a  stream  of  brilliant  sparks.     This  is  the 
principle  of  the  Ruhmkorif  coil,  which   has   been  greatly 
improved  by  Mr.  Ritchie,  of  Boston,  and  is  now  one  of  the 
most  energetic  of  electrical   machines   yet  devised,  pro- 
ducing electricity  in  large  quantity  and  of  extraordinary 
intensity. 

140. — Voltaic   electricity  will    travel    through    a    con- 


ELECTRICAL  DECOMPOSITION. 


FIG.  G2. 


ductor  thousands  of  miles  rather  than  penetrate  a  barrier  of 
air  a  small  fraction  of  an  inch  in  thickness,  while  frictional 
electricity  will  leap  through  miles  of  intervening  atmos- 
phere. For  sustained  effects,  as  in  chemical  decomposi- 
tions and  telegraphy,  where  vast  quantities  of  electricity 
are  required,  the  battery  is  employed,  its  current  being 
raised  to  the  requisite  tension  by  multiplying  the  cells. 

141.  Electrolysis. — If  the  ends  of  the  platinum  wires 
connected  with  a  battery  are  placed  near  each  other  in  a 
vessel  of  water  containing  a  little  sulphuric 
acid  to  aid  conduction,  bubbles  of  gas  will 
be  seen  to  rise  from  the  terminals  and  es- 
cape at  the  surface.  A  couple  of  glass 
tubes  filled  with  water,  and  inverted  in  the 
vessel  over  the  poles,  serve  to  collect  the 
rising  gases,  Fig.  62,  which,  upon  examina- 
tion, prove  to  be  pure  hydrogen  and  pure 
oxygen,  the  bulk  of  the  former  being  twice 
that  of  the  latter.  The  source  of  the  gases 
is  the  water  which  is  decomposed.  This 
operation  is  termed  electrolysis  (analyzing 
by  electricity),  and  any  substance  that  is 
capable  of  this  decomposition  is  called  an  electrolyte. 

142. — When  compounds  are  electrolvzed,  their  ele- 
ments are  found  in  opposite  electrical  states.  Some,  as 
oxygen,  chlorine,  sulphur,  appear  at  the  positive  electrode, 
and  are  called  electro-negative  bodies ;  while  others,  as 
hydrogen  and  the  metals,  appear  at  the  negative  electrode, 
and  are  called  electro-positive.  Oxygen  heads  the  first 
list,  or  is  the  most  powerful  electro-negative  body,  while 
the  newly-discovered  caesium  heads  the  other,  being  the 
strongest  electro-positive  substance.  The  elements  may 
be  arranged  in  such  an  order  that  each  will  be  electro- 
negative to  all  which  follow  it,  and  electro-positive  to  all 
which  precede  it.  As  the  electric  current  thus  originates 
in  chemical  changes  and  produces  them,  and  as  the  atoms 


76 


CHEMICAL  PHYSICS. 


FIG. 


seem  to  be  in  opposite  electrical  states,  it  is  obvious 
that  electrical  force  is  very  closely  allied  to  chemical 
power. 

143.  Electrotype.— When  a  salt  of  copper,  silver,  nickel, 
or  gold,  is  dissolved  in  water,  if  a  current  of  electricity  be 
passed  through  the  liquid,  it  decomposes  the  saline  body, 
and  the  metal  is  deposited.  In  this  way  medals  may  be 
copied  (electrotype) ;  or  new  metallic  surfaces  may  be 
imparted  to  articles,  as  in  electro-gilding  and  electro- 
plating. 

144.  Heating  Effects  of  the  Current— 
A  current  passing  through  a  conductor 
raises  its  temperature  in  proportion  to 
the  electricity  arrested.  A  wire  which 
is  but  little  heated  by  a  current,  if  con- 
siderably reduced  in  diameter,  becomes 
instantly  white  hot.  The  arrested  elec- 
tricity appears  as  heat.  Two  carbon 
points  brought  into  contact  in  the  circuit, 
arid  then  slightly  separated,  emit  a  light 
of  dazzling  splendor,  Fig.  63,  known  as 
Electric  Light.  the  electric  light. 

§  4.    Electricity,  Magnetism,  and  Heat. 

145.  Electro  •  Magnetism. — If    a   magnetic   needle   be 

brought  near  a   wire   along  which  an  electric  current  is 

passing,  the  needle  will  be  caused  to  move.     The  degree 

FlG  64  of  the  motion  will  depend  upon  the 

|+Jt >  strength    of    the    current,    and   its 

~lj\  direction  upon  the  relative  position 
of  the  needle  and  wire.  If  the 
wire  be  above  and  parallel  to  the 

Current  and  Needle. 

needle,  the  pole  next  the  negative 

electrode  will  move  westward ;  if  beneath  the  needle, 
it  will  move  eastward.  If  the  wire  is  on  the  east  side, 


f 


ELECTRO-MAGNETISM.  77 

this  pole  will  be  elevated  ;  if  on  the  west,  it  will  be  de- 
pressed. In  all  cases  it  tends  to  place  itself  at  right  an- 
gles, or  transverse,  to  the  wire.  If  the  wire  be  bent,  so  as 
to  pass  above  and  below  the  needle,  Fig.  64,  the  effect  is 
increased ;  and,  if  it  be  coiled  round  many  times  in  the 
same  manner,  it  becomes  still  more  powerful. 

146,  The  Astatic  Needle. — A  single  needle  keeps  its 
place  in  the  magnetic  meridian  with  considerable  force,  so 
that  a  very  faint  current  will  not  move   it ;  but,  if  two 
needles  are  placed  parallel,  near  each  other,  with  reversed 
poles,  their  directive  force  is  mutually  neutralized.     Two 
needles  thus  fixed  upon  an  axis,  Fig.  65,  form  the  astatic 
(unstable)   needle.      If  one   is   slightly 

stronger  than  the  other,  it  still  retains 

a  feeble  tendency  to  keep  its  north  and 

south  position.      If,  now,  the   wire  of 

Fig.  65  were  folded  round  both  these 

needles,  the  same  current   would  urge 

them  in  opposite  directions,  and  there 

would  be  no  motion ;  but,  when  the  coil          Astatic  Needle. 

incloses  only  one  of  the  needles,  as  the 

lower,  for  example,  the  current  impels  both  needles  in  the 

same  direction.     If  the  needles  be  suspended  by  a  single 

fibre  of  silk,  it  affords  the  means  of  detecting  the  faintest 

electrical  current,  and  forms  the  galvanometer. 

147.  Thermo-Electricity.— Heat,  applied  to  unlike  met- 
als when  in  contact,  produces  a  current  known  as  thermo- 
electricity.    A  B,  Fig.  66,  is  a  bar  of  antimony,  and  B  C 
a  bar  of  bismuth,  soldered  together  at  one  extremity,  and 
connected  by  the  wire  D  at  the  other.     When  the  place 
of  junction  is   warmed,  an  electric  current  is  produced, 
which  moves  in  the  direction  of  the  arrows.     If  the  junc- 
tion B  is  chilled,  the  current  moves  in  the  opposite  direc- 
tion.    Such   a  combination  forms  a    thermo-electric  pair. 
The  effect  is  increased  if  several  of  these  are  united,  form- 
ing what  is  known  as  the  thermo-electric  pile.     To  secure 


78 


CHEMICAL   PHYSICS. 


FIG.  66. 


a  compact  arrangement,  they  are  soldered  together,  and 
combined  as  in  Fig  67,  A  representing  one  of  the  faces 
of  the  pile.  When  both  faces  are  equally 
heated,  there  is  no  current.  If  the  face,  A, 
is  warmed,  there  is  a  current  in  one  direc- 
tion, due  to  the  difference  of  temperatures 
between  the  two  faces.  If  the  opposite  face 
,  is  warmed,  or,  what  is  the  same  thing,  if 


Thermo  electric  Pair. 


Arrangement  of  the  Bars. 


the  face,  A,  is  cooled,  there  is  a  reverse  current. 

148.   In  Fig.   68,  A  B   represent   the   thermo-electric 
pile  as  mounted  for  lecture-room  use.     A   shows  one  of 


FIG.  63. 


Thermo-electric  Pile  as  mounted  for  Use. 

the  faces ;    w  w  are  wires  connecting  it  with  the  galva- 
nometer,    The  needle  in  n  is  suspended  by  a  fibre  of  un- 


ACTION  OF   THE   GALVANOMETER.  79 

spun  silk,  s  s,  and  protected  from  currents  of  air  by  the 
glass  shade  G.  To  one  end  of  the  needle  is  fixed  a  piece 
of  red  paper,  and  to  the  other  a  piece  of  blue.  If  the  face 
of  the  pile  is  merely  breathed  upon,  the  warmth  swings 
the  needle  round  to  90°,  or  at  right  angles  to  the  cur- 
rent— the  pieces  of  paper  making  the  movement  visible 
throughout  the  room.  This  important  instrument  detects 
heat  radiation  from  sources  much  lower  than  the  human 
body,  and  announces  the  heat  emitted  from  the  bodies  of 
insects.  Lately  it  has  been  used  to  detect  the  heat  from 
the  fixed  stars. 

148a.  Animal  Electricity,— Certain  fish  possess  the  re- 
markable power  of  giving  electrical  shocks.  They  have 
internal  organs  for  this  purpose,  which  play  the  part  of 
batteries,  and  the  discharges  from  them  produce  all  the 
effects  of  ordinary  electricity.  In  the  torpedo  the  electri- 
cal organs  are  situated  on  each  side  of  the  head,  and  con- 
sist of  a  mass  of  cells  filled  with  a  dense  fluid  consisting 
of  water,  albumen,  and  common  salt.  These  organs  give 
rise  to  electricity  just  as  the  muscles  do  to  mechanical  mo- 
tion. A  dense  mass  of  nerves  links  them  with  the  brain, 
which  controls  the  electrical  discharges  in  the  same  way 
as  it  does  the  mechanical  movements. 

It  has  been  proved  that  currents  of  electricity  circulate 
in  the  frames  of  all  animals,  and  that  different  parts  or 
sections  of  the  muscles  are  in  different  electrical  states. 
The  smallest  shreds  of  muscular  tissue  have  been  proved 
by  Prof.  Du  Bois-Raymond  to  manifest  currents,  the  longi- 
tudinal section  being  alwa\rs  positive  to  the  transverse  sec- 
tion. By  arranging  a  series  of  half-thighs  of  frogs,  alter- 
nately connecting  the  exterior  and  interior  surfaces,  he  ob- 
tained an  electrical  current  that  decomposed  potassic  iodide, 
deflected  a  magnetic  needle  90°,  and  caused  the  gold  leaves 
of  an  electroscope  to  diverge.  Many  have  supposed  that 
the  nervous  force  is  electrical,  but  this  is  disproved  by  the 
comparatively  slow  rate  of  its  motion.  It  is,  however, 
probably  an  analogous  polar  force. 


CHAPTER  V. 

LIGHT. 

§  1.  Motion  of  the  Radiant  Forces. 

149.  Their  Motion.— Light  is  that  agent  which,  acting 
on  the  eye,  produces  vision.     Other  forces   are   generally 
associated  with  it  that  obey  the  same  laws  of  motion ;  and, 
as  that  motion  is  in  rays,  they  are  known  as  radiant  forces  ; 
their  laws  of  movement  are   the  same.     Light  moves  in 
straight  lines  and  in  all  directions  from  the  point  of  emis- 
sion— diminishing  in  intensity  in  inverse  ratio  to  the  square 
of  the  distance.     Its  velocity  is  about  190,000  miles  per 
second.     When   light   falls  upon   bodies,  some    reflect  it, 
others  absorb  it,  and  others  transmit  it.     The  laws  of  these 
motions  are  explained  in  books  upon  optics. 

150.  The  Analysis  of  Light. — By  the  prism — a  triangu- 
lar piece  of  glass,  or  other  transparent  substance — the  white 
ray  is  decomposed  into  a  series  of  colors.     A  beam  of  solar 
light  passing  through  such  a  prism,  Fig.  69,  is  refracted  by 

it,  and  produces  an  oblong 
Fl°- 69>  colored    image    called    the 

solar  spectrum.  It  is  usu- 
ally considered  to  comprise 
the  seven  colors  enumer- 
ated in  the  accompanying 
diagram.  White  light  is, 
therefore,  held  to  be  a  com- 

pound  consisting  of  these  colored  lights,  which  are  only 
separated  by  the  prism.     Each  color  has  its  own  peculiar 


ANALOGIES   OF   LIGHT   AND   SOUND.  81 

refrangibility,  or  degree  of  divergence  from  the  original 
source,  the  red  being  least  refracted,  and  the  violet  most. 
Certain  of  the  rays  accompanying  light  produce  heating 
effects,  and  others  chemical  effects.  These  rays  are  gov- 
erned by  the  same  laws  of  motion  as  light  itself,  but  by 
the  prism  the  heat  is  mainly  distributed  through  the  red 
end  of  the  spectrum,  and  the  chemical  force  through  the 
violet  extremity.  (162.) 

151.  The  Wave  Hypothesis. — The  motion  of  the  ra- 
diant forces   is   explained    by  what   is   called   the  wave- 
theory.     It  is  known  that  sound  is  propagated  through 
the  air  by  means  of  the  vibration  of  its  particles ;  and  it 
is  supposed  that  light  moves  by  a  similar  mode  of  action. 
There  is  a  great  amount  of  evidence  to  show  that  the 
radiant  forces  are  propagated  by  some  kind  of  undulatory 
movement,  but  the  hypothesis  implies  a  medium  that  is 
capable  of  this  kind  of  motion.     This  medium  is  assumed 
to  be  an  infinitely  rare  and  elastic  ether  that  fills  all  space 
and  pervades  all  matter. 

152.  Cause  of  Colors. — According  to  this   hypothesis, 
light  is  transmitted  by  ethereal  undulations  just  as  sound  is 
by  those  of  the  atmosphere ;  with  only  this  difference,  that, 
while  the  air-particles  move  backward  and  forward  in  the 
same  direction  as  the  advancing  wave  (longitudinal  vibra- 
tions), the  ethereal  particles  move  across  the  course  of  the 
wave  (transverse  vibrations).     Thus  the  spectrum  is  to  the 
eye  what  the  gamut  is  to  the  ear.     As  the  pitch  of  sound 
depends  upon  the  length  of  the  air-wave,  so  the  color  of 
light  depends  upon  the  length  of  the  ethereal  wave;  and 
as  loudness  of  sound  depends  upon  the  extent  of  the  Swing 
of  air-particles,  so  the  brightness  or  intensity  of  color  re- 
sults from  the   extent  of  the  excursions  of  the  ethereal 
particles. 

By  several  refined  methods  which  cannot  be  detailed 
here,  the  lengths  of  the  ethereal  waves  upon  which  colors 
depend  have  been  estimated.  The  motions  which  produce 


82  CHEMICAL  PHYSICS. 

red  are  slower,  and  the  undulations  longer  than  those 
which  produce  violet.  It  is  found  that  40,000  waves  of 
red  light  would  measure  an  inch,  while  60,000  waves  of 
violet  light  would  fill  the  same  space.  The  other  colors 
are  intermediate,  their  number  of  waves  increasing  grad- 
ually from  red  to  violet.  As  light  moves  190,000  miles 
per  second,  that  length  of  ray  streams  into  the  eye  each 
second.  If  this  distance  be  reduced  to  inches,  and  the 
product  be  multiplied  by  40,000,  we  shall  have  the  number 
of  waves  which  beat  against  the  retina  each  second,  when 
we  look  upon  a  red  color.  If  the  same  product  is  multi- 
plied by  60,000,  we  get  the  number  of  pulses  per  second 
which  strike  the  retina  when  looking  upon  a  violet  color. 

153,  Transmission  of  Radiant  Motion. — In  this  view  it 
is  necessary  to  distinguish  between  vibrations  and  undula- 
tions.    In  the  case  of  sound,  the  vibrations  of  a  sonorous 
body,  as  a  bell,  produce  undulations  in  the  air  which,  when 
striking  against  distant   bodies,  may  set  them   also  into 
vibration.     The  vibrations  of  the  bell,  transmitted  as  air- 
waves, are  taken  up  by  the  tympanum  of  the  ear,  which, 
when  set  to  vibrating,  gives  rise  to  the  sensation  of  sound. 
So  the  vibration  of  atoms  in  a  flame  produces  undulations 
in  the  ether ;  these  are  transmitted  to  the  nerve  of  vision, 
and,  breaking  against  it,  throw  its  atoms  into  the  vibi^- 
tions  which  produce  sight.     In  the  same  way  the  particles 
of  a  heated  body  are  supposed  to  be  in  a  state  of  vibra- 
tion, which  are  transmitted  by  ethereal  undulations,  and 
these,  falling  upon  other  bodies,  set  their  particles   into 
vibration,  and  raise   their  temperature.      This  is  the  ex- 
planation afforded  of  radiant  heat. 

§  2.    Interference  and  Polarization. 

154.  Interference  of  Waves, — When  two  sets  of  water- 
waves  are  made  to  flow  together,  if  they  coincide,  that  is, 
if  ridge  corresponds  to  ridge,  their  height  will  be  increased; 


INTERFERENCE  OF   WAVES. 


83 


PIG.  70. 


but,  if  the  ridge  of  one  corresponds  with  the  trough  of  an* 
other,  they  will  neutralize  each  other,  and  the  water  be- 
come still.  This  is  called  interference. 

Again,  two  stretched  strings,  or  two  tuning-forks,  may 
be  so  placed,  that,  when  simultaneously  struck,  they  do 
not  give  forth  a  continuous  sound ;  but  there  is  produced 
a  series  of  alternating  swells  and  depressions  of  tone. 
During  the  pauses,  there  is  still  rapid  vibration,  so  it  is 
certain  that  the  sounds  are  extinguished  by  interference 
of  their  waves. 

155.  Interference  of  Light. — If  a  beam  of  colored  light 
be  admitted  into  a  dark  room  by  two  pin  holes  made  near 
each  other  in  a  thin  sheet  of  metal,  and  be  made  to  fall 
upon  a  screen  at  a  short  distance,  the  rays  intersect  each 
other,  and  a  series  of  dark  bands  alternating  with  bright 
stripes  will  be  formed  upon 
the  screen  by  interference  of 
the  ray  from  the  two  orifices. 
In  Fig.  70,  a  f  represent  the 
two  pinhcles,  and  c  d  e  b  a 
portion  of  the  screen,  c  g  be- 
ing a  line  joining  the  two 
surfaces  at  right  angles,  and 
midway  between  the  pin- 
holes.  The  rays,  a  C,  f  C,  Interference  of  Light. 

pass   through    equal    paths ; 

their  waves  coincide  at  c,  and,  heightening  each  other's 
effect,  a  bright  band  is  produced  at  c  ;  a  d^fdwill  differ 
by  the  length  of  one  wave,  a  e,fe  by  the  length  of  two 
waves,  and  a  6,  f  b  by  the  length  of  three  waves  ;  hence, 
there  will  be  also  bright  bands  at  rf,  e,  and  b.  But  the 
rays  from  the  two  orifices,  meeting  at  1,  2,  3,  differ  in 
length  successively  by  half  a  wave,  a  wave  and  a  half,  and 
two  waves  and  a  half,  and,  by  thus  interfering,  extinguish 
each  other  and  produce  darkness.  As  the  rays  which  meet 
ut  c  are  equal,  it  is  obvious  that  all  the  other  rays  coming 


84  CHEMICAL  PHYSICS. 

from  a  are  lengthened,  and  all  others  coming  from  f  are 
shortened.  As  this  variation  of  length  is  gradual,  there 
will  be  a  gradual  passage  from  the  brightest  light  to  com- 
plete darkness.  This  effect  is  exhibited  by  the  shaded 
portion  of  the  diagram.  If  the  light  from  one  aperture  is 
intercepted,  all  the  dark  bands  disappear. 

Thus  we  have  seen  that  motion  added  to  motion  pro- 
duces rest ;  that  sound  added  to  sound  produces  silence ; 
that  light  added  to  light  produces  darkness ;  and  it  has 
also  been  proved  that  heat  added  to  heat  produces  cold, 
heat-rays  being  liable  to  interference,  like  light. 

156.  Polarization  of  Light.— When  light  is  reflected  at 
certain  angles  from  the  surface 

r  IG-  71. 

of  glass,  water,  marble,  polished 
wood,  etc.,  a  portion  of  it  under- 
goes a  remarkable  change.  Al- 
though taking  place  all  around 
us  constantly,  we  do  not  per- 
ceive it,  but  it  may  be  detected 
in  various  wrays.  Two  plates  of 
glass  are  blackened  on  one  side 
so  as  to  have  but  a  single  re- 
flecting surface,  and  then  placed 
FlG  73  as  shown  in  Fig.  71,  <7,  5,  with 

their  edges  toward  the  eye.  A 
ray  of  common  light  falling  upon 
a  in  the  direction  of  the  arrow 
is  reflected,  and,  upon  being 
-74.  thrown  upon  &,  is  again  reflect, 

ed.     The  ray  is  changed  at  a,  as 
the  altered  structure  of  the  line 
shows,  but  the  effect  is  not  ap- 
parent.    If  now  &,  or  the  second 
Light  polarized  by  Reflection.       platej  is  turned  a  quarter  round, 
its  angle  with  the  ray  being  preserved,  reflection  ceases, 
and  the  beam  is  extinguished,  Fig.  72.    Turning  it  anothei 


POLARIZATION  OF   LIGHT. 


85 


quarter  round,  Fig.  73,  the  ray  is  again  reflected;  and  still 
another  quarter  revolution,  Fig.  74,  brings  it  on  the  oppo- 
side  side  to  Fig.  71,  and  again  extinguishes  it.  The  beam 
may  be  reflected  from  surface  to  surface  any  number  of 
times  in  the  same  plane  •  but  it  has  lost  the  ability  of 
being  reflected  in  planes  at  right  angles  to  that  plane, 
while  common  light  may  be  reflected  in  all  directions.  It 
thus  appears  that  the  ray  has  acquired  different  properties 
on  different  sides.  From  its  analogy  to  magnetic  polarity, 
this  change  is  called  polarization,  and  the  ray  thus  affected 
is  said  to  be  polarized.  The  angle  at  which  the  ray  falls 
upon  the  polarizing  surface  is  called  the  polarizing  angle, 
and  differs  in  different  substances  :  for  glass,  it  is  56°  45', 
while  for  water  it  is  53°  11'. 

157.  Polarizing  by  Transmission,— 
Light  transmitted  obliquely  through  a 
bundle  of  thin  glass  plates,  Fig.  75,  is 
polarized,  and  the  same  effect  is  also 
produced  by  its  passage  through  certain 
crystals.  A  stone,  called  the  tour  IK  a- 
line,  is  much  used  for  polarizing  pur- 
poses. A  thin  polished  plate  of  it  po- 
larizes the  light  which  passes  through 
it,  as  in  Fig.  76.  If  a  second  plate  is 
placed  parallel  to  the  first,  Fig.  77,  the  light  passes 


FIG.  75. 


Polarization  by  Thin 
Plates. 


FIG.  7( 


FIG.  77 


FIG.  78. 


Polarization  by  Tourmalines. 


through  both  ;  but  if  the  second  plate  is  turned  a  quarter 
round,  Fig.  78,  the  light  is  stopped.  "  The  rays  of  the 
meridian  sun  cannot  pass  through  a  pair  of  crossed  tour- 


86 


CHEMICAL   PHYSICS. 


FIG.  79. 


malines."  The  plate  polarizing  the  light  is  called  a  polar- 
izer /  that  which  tests  or  detects  it  after  it,  is  changed,  is 
termed  the  analyzer. 

158.  Theory  of  Polarization.— The    wave-theory   thus 
explains  the  phenomena.     We  can  vibrate  a  cord  up  and 

down,  horizontally, 
or  in  any  direction 
transverse  to  its 
length,  Fig.  79.  In 
common  light  the 
undulations  take 
place  practically  in  all  these  directions  at  once.  It  has 
been  suggested  that  common  light  may  be  represented  by 
a  round  rod  ;  polarized  light  by  a  flat  lath.  Supposing 


Vibration  in  Different  Planes. 


FIG.  80. 


FIG.  81 


FIG.  82. 


Illustrations  of  Planes  of  Vibration. 

the  round  rod  to  image  to  us  the  common  ray,  the  radii, 
Fig.  80,  will  exhibit  the  system  of  transverse  vibrations 
taking  place  in  all  planes.     But  the  effect  is  just  the  same 
if   we    regard    the  vibrations   as  taking 
place  in  two  planes  only,  at  right  angles 
to  each  other,  as  in  Fig.  81.     Now,  when 
common  light  is  reflected  in  certain  po- 
sitions, which  we  have  just  noticed,  one 
of  its  planes  of  vibration  is  destroyed, 
Motion  in  a  Single       and  the  beam  is  polarized,  its  vibrations 
taking  place  all  in  one  plane,  Fig.  82. 
We  can  now  easily  understand  the  action  of  the  tourma- 
line upon  light.     A  plate  of  this  crystal  suppresses  one  of 
the  planes  of  vibration,  and  therefore  transmits   a  polar- 


POLARIZATION  AND   REFRACTION. 


87 


ized  ray.  This  will  pass  through  a  second  plate  if  it  is 
held  in  such  a  manner  that  its  structure  coincides  with  the 
motion  ;  but.  if  it  is  turned  so  as  to  cross  the  waves,  the 
ray  is  obstructed.  A  card  which  readily  slips  through  a 
grate  when  its  plane  coincides  with  the  bars,  will  be 
stopped  if  it  is  turned  a  quarter  round,  Fig.  83. 

159. — When  a  ray  falls  upon  a  transparent  surface  at 
a  certain  angle,  its  planes  of  vibration  are  resolved  into 


FIG.  84. 


Fio.  85. 


Polarized  Eays. 


Double  Refraction. 


FIG.  86. 


two,  one  of  which  is  reflected,  and  the  other  transmitted. 
Fig.  84 ;  both  are  polarized,  but  one  ray  vibrates  in  one 
direction,  and  the  other  at  right  angles  to  it. 

160.  Double   Refraction.— Some 
substances  possess  the  singular  prop- 
erty of  splitting  the  ray  which  passes 
through   them,  producing  an   effect 
which   is   known  as  double  refrac- 
tion. Fisr.    85.      Iceland    spar    and 

Effect  of  Double  Refraction. 

many  crystals  possess  this  power; 

printed  words,  or  a  candle-flame,  seen  through  them,  ap- 
pearing double,  Fig.  86.  The  effect  is  supposed  to  be  due 
to  the  molecular  structure  of  the  body. 

161.  Phosphorescence. — This  is  a  property  possessed  by 
various  bodies  of  emitting  a  faint  light  at  ordinary  or  low 
temperatures,   and   is   so  named  from   phosphorus,  which 
exhibits  it  in   a   remarkable   degree.     Phosphorescence  is 
manifested  by  certain  insects,  as  the  firefly  and  glow-worm, 
by  several  species  of  plants,  by  various  animal  and  vege- 


88  CHEMICAL   PHYSICS. 

table  substances  in  a  state  of  decay,  and  by  exposure  of 
many  substances  to  sources  of  light.  If  calcined  oyster- 
shells  be  placed  for  a  short  time  in  sunshine,  and  then 
withdrawn  into  darkness,  they  will  continue  to  glow  for 
some  time,  while  other  bodies,  as  the  diamond  and  chloro- 
phane,  after  exposure,  remain  for  a  long  time  luminous. 
Recent  investigations  have  shown  that  the  same  property 
exists  in  a  much  lower  degree  in  a  great  number  of  bodies, 
their  phosphorescence  continuing  in  most  cases  for  the 
briefest  moment — sometimes  only  for  the  ten-thousandth 
of  a  second.  It  would  seem  that,  in  cases  where  the  lu- 
minosity continues,  the  molecules  of  matter  are  set  in  mo- 
tion by  the  ethereal  undulations,  and  continue  to  move 
after  the  withdrawal  of  the  exciting  cause.  Fluorescence 
is  a  kind  of  phosphorescence,  in  which  the  highly-refrangi- 
ble dark  rays  of  the  solar  spectrum,  next  to  be  considered, 
are  turned  to  light  when  falling  upon  certain  substances, 
as  fluor-spar,  or  sulphate  of  quinine  solution. 


CHAPTER   VI. 

THE     CHEMISTRY     OF     LIGHT. 

§  1.   The  Chemical  Rays. 

162.  A  Third  Radiant  Force.  —  Besides  the  heat-rays, 
which  take  effect  upon  all  kinds  of  matter,  and  the  lumi- 
nous rays,  which  act  only  upon  special  forms  of  nerve- 
substance  producing  the  sensation  of  vision,  there  is  a 
third  class  of  rays  which  act  upon  certain  chemical  bodies, 
producing  combination  and  decomposition.  These  have 
been  called  actinic  rays,  and  the  agency  actinism /  but 
they  are  better  known  as  chemical  rays.  They  accompany 
the  light  of  the  sun  and  stars,  and  are  produced  in  arti- 


THE   CHEMISTRY   OF  LIGHT. 


89 


FIG.  87. 


ficial  illumination ;  but  they  are,  nevertheless,  distinct 
from  light.  The  art  of  photography  depends  upon  them, 
and  has  given  a  great  stimulus  to  their  recent  investiga- 
tion. Like  light  and  heat,  the  chemical  radiations  are 
measurable  in  their  effects,  and  have  given  rise  to  an  in- 
dependent branch  of  scientific  inquiry. 

163.  Refrangibility  of  the  Invisible  Radiations.  —  The 
heat-rays  and  the  chemical  rays  are  reflected  and  refracted 
like  light,  and  like  the  colored  rays  the}'  exhibit  marked 
differences  in  their  degrees  of  refrangibillty.  When  the 
sunbeam  is  passed 
through  a  prisrn 
(Fig.  87)  not  only 
is  there  an  oblong 
visible  image 
thrown  upon  the 
screen,  but  there 
is  also  an  invisi- 
ble heat  -  image, 
and  an  invisible 
chemical  image, 
which  are  revealed 
in  different  ways. 
The  position  and 
varying  intensity 
of  the  heat-spec- 
trum  may  be 
traced  out  by  a 
delicate  galvanom- 
eter, and  it  is  found  that  it  begins  down  in  the  neigh- 
borhood of  a,  and  runs  up  into  the  luminous  region.  A 
large  portion  of  the  heat-rays  are  hence  of  a  lower  refrangi- 
bility  than  the  red,  and  are  dark  radiations.  If,  now,  a 
solution  of  argentic  nitrate  is  washed  over  a  large  sheet  of 
paper,  which  is  then  placed  upon  the  screen  so  as  to  re- 
ceive the  visible  spectrum  and  extend  through  the  space 


Positions  of  the  Three  Spectra. 


90  CHEMICAL   PHYSICS. 

above  it,  a  chemical  change  takes  place  upon  its  surface, 
producing  a  blackening,  which  defines  the  outline  of  the 
chemical  spectrum.  It  is  now  found  that  the  chemical 
rays  are  more  refrangible  than  the  luminous  ;  and  that, 
while  the  blackening  takes  place  in  the  colored  spectrum, 
it  extends  also  through  the  dark  space  up  to  b.  That  the 
heat  of  the  spectrum  is  greatest  in  the  red,  and  that  there 
are  dark  thermal  rays  of  still  lower  refrangibility,  was  shown 
by  Sir  William  Herschel,  in  the  year  1800.  That  the  chem 
ical  rays  of  the  luminous  spectrum  are  most  active  in  the 
violet  region  was  pointed  out  by  Scheele,  in  1777;  while 
their  extension  into  the  dark  space  beyond,  was  discov- 
ered by  Ritter,  in  1801. 

164.  Distribution  of  the  Forces.— The  forces  of  the  spec- 
trum are  thus  very  unequally  distributed,  as  is  illustrated 
in  Fig.  88,  where  they  appear  to  rise  like  the  peaks  of 
mountains.  The  middle  curve  shows  the  varying  intensitv 


Varying  Intensities  of  the  Spectrum  Forces 


of  the  luminous  force.  The  maximum  is  at  B  in  the  yel- 
low space,  and  from  this  point  the  intensity  of  the  light 
rapidly  declines  each  way  ;  its  extent  being  shown  by  the 
space  shaded  with  oblique  lines.  The  curve  A,  with  the 
vertical  lines,  represents  the  position  and  varying  force  of 
the  heat;  and  the  curve  (7,  horizontally  shaded,  exhibits 
the  distribution  and  unequal  energy  of  the  chemical  force. 
The  three  maxima  are  widely  separated,  as  if  there  were 
some  antagonism  among  them ;  and  it  is  noticeable  that 
where  the  light  is  strongest  the  chemical  force  seems  quite 


THE   CHEMISTRY   OF  LIGHT.  91 

neutralized.  Different  kinds  of  prisms  (180)  give  some- 
what different  effects,  but  do  not  change  their  order.1  The 
mode  of  action  of  all  these  radiations  is  unquestionably 
the  same.  Heat-rays,  light-rays,  and  chemical  rays,  differ 
from  each  other  only  as  yellow  differs  from  green,  that 
is,  by  wave-length  and  intensity  of  vibration.  They  all 
exhibit  the  effects  of  interference  and  polarization  which 
proves  the  mode  of  ray-action  to  be  alike  in  all. 

165.  Actinoinetry. — It  has  been  stated  that  the  chemi- 
cal rays  are  measurable  in  their  force,  and  for  this  impor- 
tant step  of  research  we  are  indebted  to  Dr.  J.  W.  Draper. 
If  hydrogen  and  chlorine  gases  be  mixed  in  equal  propor- 
tions in  a  glass  vessel,  and  kept  in  the  dark,  they  will  not 
combine  ;  but,  if  exposed  to  the  light,  they  unite  with  each 
other,  forming  a  compound.     Upon  such  a  mixture,  how- 
ever, the  red  rays  produce  no  effect,  while  the  violet  rays 
cause  the  gases  to  combine  explosively.     It  is  the  chemi- 
cal rays  that  are  here  active,  and  Dr.  Draper  employed  a 
mixture  of  these  gases  to  test,  by  the  rate  of  combination, 
the  varying  intensity  of  the  force.     Instruments  for  this 
purpose  have  been  called  actinometers.     Roscoe  and  Bun- 
sen  afterward  employed  papers,  made  sensitive  by  silver 
nitrate,  which  were  blackened  in  given   times   to  certain 
shades  as  standard  tests  of  the  varying  force  of  the  chemi- 
cal rays. 

166.  Variation  of  Chemical  Rays  in  England.— Observa- 
tions were  made  at  the  Kew  Observatory,  near  London,  to 
determine  the  changes  of  chemical  activity  in   the  solar 
rays  at  different  hours  of  the  day,  and  different  seasons  of 
the  year.     The  diagram   (Fig.  89)  represents  the  results 
graphically.     The  experiments  were  made  from  6  A.  M.  to 
6  P.  M.  throughout  the  year  1866.     The  figures  below  give 
the  hour  of  the  day,  and  each  curve  represents  the  daily 
change  in  intensity  for  the  average  of  a  month — the  hori- 
zontal lines  marking  the  scale  of  effects.     The  maximum 
effect  occurs  at  twelve  o'clock,  and  the  forenoon  rise  and 

1  See  note  on  this  subject  in  the  Appendix. 


CHEMICAL  PHYSICS. 


Curves  of  Variation  at  Kew. 


afternoon  decline  are  very  nearly  equal.    But  by  comparing 
the  highest  and  lowest  curves  it  will  be  seen  that  the  chem- 
FrG  89  ical  intensity  was  fully 

seven  times  as  great 
in  July  as  in  Decem- 
ber. 

167.  Effects  at  the. 
Equator.  —  As  we  go 
south,  though  the  light 
increases  in  brilliancy, 
the  chemical  action  is 
impeded  or  interfered 
with,  so  that  it  is  said 
to  take  ten  or  twenty 
times  longer  to  get  a 
picture  under  the  blaze  of  the  Mexican  sun  than  in  New 
York.  Yet  tlie  effect  seems  not  due  to  lack  of  intensity 
of  the  chemical  rays, 
but,  perhaps,  to  some 
obscure  cause  of  irreg- 
ular action.  Fig.  90 
represents  the  effects 
obtained  at  Para,  in 
North  Brazil,  situated 
nearly  under  the  equa- 
tor. The  zigzag  lines 
show  the  sudden  chan- 
ges of  intensity  from 
hour  to  hour,  which 
were  accompanied  by 
heavy  showers.  The 
dotted  line  below  rep- 
resents the  chemic  alre- 

Sults     at     Kew    at     the  Fluctuations  at  the  Equator. 

same  time. 

168.  Relation  to  Vegetation.— Of  the  effects  produced 


FIG.  90. 


THE   CHEMISTRY   OF   LIGHT.  93 

by  these  rays  in  Nature  little  is  understood.  It  has  long 
been  known  that  light  exerts  a  powerful  influence  upon 
the  organic  world.  Vegetation  languishes  in  the  absence 
of  light,  and  flourishes  when  exposed  to  it.  It  was  at  first 
supposed  that  this  power  over  plants  resided  in  the  chemi- 
cal ravs  ;  but  it  is  now  known  that  the  force  that  decom- 
poses carbon  dioxide  in  green  leaves,  and  which  is  the 
foundation  of  the  vegetative  processes,  is  most  active,  not 
in  the  blue,  but  in  the  yellow  space  of  the  spectrum,  where 
the  actinic  force  is  absent. 

§  2.  Photographic  Chemistry. 

169.  Chemical  Eeactions  of  Light.  —  It  was  long  sup- 
posed that  the  chemical  rays  act  only  upon  a  few  sub- 
stances, but  the  contrary  is  really  the  fact.     So  many  sub- 
stances are  affected  by  it,  and  in  so  many  different  ways, 
that  some  think  a  ray  of  light  cannot  fall  upon  the  surface 
of  any  solid  without    impressing  upon  it  an  enduring  mo- 
lecular change.     Four  kinds  of  effect  may  be  here  referred 
to :  First,  the  elements,  such  as  phosphorus,  are  altered  by 
light  in  their  allotropic  forms  (271).  Second,  light  promotes 
chemical  combination    of  the   elements,  as  already  shown 
(165).     Third,  it  produces  mechanical  effects.    If  the  beau- 
tiful ruby-colored  crystals  of  arsenic  disulphide  are  exposed 
to  light  for  some  months,  they  become   pliant  and  fall  to 
powder.     Fourth,  chemical    compounds,  as  silver  nitrale, 
are  decomposed  under  the  influence  of  light,  and  new  com- 
pounds are  formed. 

170.  Substances  at  the  Basis  of  Photography.  —  By  ex- 
ploring this  subject,  chemists  have  founded  a  new  art  of 
great  importance,  that  of  taking  pictures  quickly,  cheaply, 
and   accurately,  by  the   direct   action    of   light.     Experi- 
menters began  to  feel  their  way  toward  this  result  early  in 
the  present  century ;  but  the  process  only  became  success- 
ful in  the  hands  of  M.  Daguerre,  a  Frenchman,  who  made 
it  public  in  August,  1839 ;  and  since  then  it  has  undergone 


94 


CHEMICAL   PHYSICS. 


FIG.  91. 


the  most  rapid  extension  and  development.  For  photo- 
graphic purposes  the  salts  of  silver  are  mainly  used — sil- 
ver iodide,  bromide,  and  chloride,  being  the  substances  most 
generally  employed.  The  unequal  susceptibility  of  these 
compounds  to  the  action  of  light  gives  great  resources  to 
the  operator,  and  is  the  basis  of  this  modern  art. 

171.  Production  of  the  Invisible  Image.  —  Photographic 
pictures  are  taken,  as  is  well  known,  by  means  of  a  camera- 
obscura,  an  instrument  by  which  inverted  images  of  ex- 
ternal objects  are 
produced  in  a  dark 
chamber  in  their 
natural  colors.  In 
Fig.  91  G  represents 
a  ground-glass  slide 
upon  which  the  im- 
age is  formed,  and 
which  is  viewed  by 
the  operator  from 
behind.  The  glass 
plate  is  brought  to 
the  exact  focus,  first 
by  sliding  the  part  M  of  the  box  in  the  part  N,  and 
then  by  turning  the  pinion  ~V,  which  moves  the  lenses  in 
the  tube  A  B.  Fig.  92  represents  the  lenses  E  L  in 
the  tube  A  B ;  two  lenses  having  the 
effect  of  allowing  a  larger  aperture, 
and  increased  light,  with  the  same  focal 
distance.  A  metallic  or  glass  plate  is 
then  prepared  in  an  obscurely  lighted 
place,  by  coating  it  with  the  proper 
chemicals,  and  it  is  then  said  to  be 
sensitive •  that  is,  it  is  very  susceptible  to  changes  from 
the  action  of  light.  It  is,  therefore,  kept  protected 
from  the  daylight,  until  substituted  for  the  glass  slide 
G  in  the  camera.  The  cap  being  then  removed  from  be- 


Photographic  Camera. 


FIG.  92. 


Position  of  Lenses. 


THE   CHEMISTRY  OF   LIGHT.  95 

fore  the  lenses,  the  light  from  the  object  to  be  taken  falls 
upon  the  sensitive  surface.  If  silver  iodide  be  used,  such 
as  Daguerre  employed,  twenty  minutes  will  be  necessary 
to  get  an  impression.  But  if  silver  bromide,  or  chloride,  be 
used,  which  are  far  more  sensitive,  the  operation  is  quick- 
ened, and  by  mixing  different  chemicals  any  degree  of  sen 
sitiveness  may  be  secured.  If  required,  an  impression 
may  be  obtained  in  the  hundredth  part  of  a  second. 

172.  Developing  the  Picture.  —  When  the  plate  is  re- 
moved from  the  camera,  no  effect  is  visible;  the  image  has 
to  be  brought  out  or  developed  by  a  subsequent  process. 
Daguerre  effected  this  by  exposing  the  plate  to  vapor  of 
mercury,    which,    being    condensed     unequally   upon   the 
changed  surface,  evolved  the  lights  and  shadows,  that  be- 
came visible  when  the  plate  was  washed  with  sodic  hypo- 
sulphite, by  which  the  unchanged  silver  iodide  is  dissolved 
away.     At  present  the  plates  exposed  in  the  camera  are 
coated  with  collodion,  in  which  the  sensitive  chemicals  are 
contained.     The  pictures   are  developed  by  washing  the 
surface  with  a  solution  of  green  vitriol,  which,  becoming 
mixed  with  the  silver  compounds,  decomposes  them,  and 
precipitates  the  silver  in  the  form  of  a  fine  black  powder, 
that  adheres  to  the  exposed  surfaces  of  the  plate. 

173.  Negatives  and  Positives.— Pictures  are  now  gen- 
erally taken  upon  a  transparent  glass  plate,  in  which  the 
lights  and  shades  are  reversed,  and  these  are  called  nega- 
tives.    But  from  these  negatives  others  are  taken,  and  the 
effects  are  again  reversed,  which  makes  them  true  to  na- 
ture— lights  answering  to  lights,  and  shadows  to  shadows : 
these   are  called  positives.      They  are  copied,  or  printed 
from  the  negative,  by  placing  sensitively-prepared  paper 
surfaces  against  the  negative,  and  exposing  to  sunlight. 
In  this  way,  from  a  single  negative,  many  positives  may  be 
obtained,  while  a  little  delicate  retouching  of  the  negative, 
with  Indian-ink  or  a  pencil,  may  remove  defects,  and  im- 
prove  all  the  positives  printed  from  it.     This  is  often  de- 


96  CHEMICAL   PHYSICS. 

sirable,  as  freckles  and  pimples  upon  the  face  are  liable  to 
be  exaggerated  in  the  photographic  negative. 

174.  Varying  Affect  of  Colored  Lights.— Yellow  and  red- 
dish light  being  chemically  inoperative,  the  artist  can  carry 
on  his  manipulations    by  a  dingy  lamp-light  or  daylight 
passing  through  yellow  glass ;  and  as  blue  light  is  chemi- 
cally most  powerful,  the  reflected   illumination  of  the  sky 
is  favorable  for  photographic   effects.     White  clouds  in- 
crease thu  chemical   intensity  of  light,  while  gray  clouds 
diminish  it.    Blue,  indigo,  and  violet  colors  generally  come 
out  light  in  photographs,  while  yellow  and  red  work  dark. 
Hence  dark-blue  flowers  on  a  light-yellow  ground  produce 
light  flowers  on  a  dark  ground.     Red,  and  also  fair  golden 
hair,  becomes  black,  and  yellow  specks  in  the  face  produce 
black  points  in  a  picture.     It  is  obvious  from  this  unequal 
working  of  light   that   mai^-colored   toilets  must  produce 
discordant   photographic  results.     "  Persons  of  dark  com- 
plexions, also  stout  persons,  should  prefer  dark  clothes;  as 
it  is  well  known  that  white  clothing  increases  in  appear- 
ance the  fullness  of  the  figure.     Thin  and  pale  persons  are 
advised,  on  the  contrary,  to  wear  light  clothes,  as  a  pale 
complexion  would  appear  even  paler  when  contrasted  with 
black."— (Vogel.) 

175.  Celestial  Photography. — The  applications  of  pho- 
tography in  the  arts  are  becoming  constantly  more  valu- 
able, and  it  is  also  an  important  resource  of   science  in 
making  quick  and  accurate  representations,  and  in  record- 
ing the  workings  of  self-registering   apparatus.     Its  astro- 
nomic indications  are  of  especial  interest.     Enlarged  pho- 
tographs of  the  moon  represent  the  details  of  its  surface 
with  surprising  minuteness  ;  and  photographs  of  the  stars 
are  taken,  which   define  their  position  with  the  greatest 
accuracy.     In  observing  eclipses  of  the  sun,  this  power  of 
producing  instantaneous   pictures   is   invaluable  ;    for  the 
display  in  a  total  solar  eclipse  is  grand,  complex,  and  mo- 
mentary— chromosphere,  prominences,  and  corona,  all  burst 


SPECTRUM   ANALYSIS. 


97 


upon  the  view  at  once,  and  baffle  every  attempt  at  delinea- 
tion. The  corona  is  a  vast,  irregular  luminous  appendage 
surrounding  the  sun,  reaching  away  to  immense  distances, 
only  visible  in  eclipses,  of  unknown  nature,  and  presenting 
the  greatest  diversity  of  aspects  at  different  times.  Pho- 
tography is  therefore  eminently  adapted  to  seize  its  pecul- 
iar and  varying  ap- 
pearances. Fig.  93 
represents  a  picture 
of  the  eclipse  of  1868, 
taken  in  a  few  sec- 
onds, and  selected 
because  its  aspect  is  £, 
very  marked.  The 
great  coronal  halo 
is  seen  to  have  the 
appearance  of  rays, 
with  deep  gaps  or 
rifts;  and  the  curious 
effect  of  an  oblique 
luminous  line  cutting  the  lower  stratum  of  light  was  re- 
corded upon  the  plate.  Other  photographs  give  a  more 
even  outline,  and  a  wider  circle  of  white  light  around  the 
central  body.  The  multiplication  of  such  impressions  in 
different  places,  and  at  different  times,  will  be  of  the  ut- 
most service  in  the  investigations  of  solar  physics. 


Photograph  of  Total  Solar  Eclipse  of  1S68. 


CHAPTER  VH. 


SPECTRUM     ANALYSIS 


176.  Interest  of  the  Subject— The  progress  of  science 
is  full  of  surprises.  A  step  is  taken  that  seems  so  wonder- 
ful that  nothing  can  surpass  it ;  but  it  is  soon  eclipsed  by 
something  still  more  wonderful.  With  the  remarkable 


98  CHEMICAL  PHYSICS. 

discovery  that  the  radiations  of  space  can  produce  endur- 
ing images  by  the  chemical  alterations  of  matter,  it  was 
thought  that  the  marvels  of  light  were  exhausted;  but, 
twenty  years  after  photography,  came  spectrum  analysis — 
the  most  brilliant  and  startling  of  all  modern  discoveries. 
It  has  endowed  the  chemist  with  a  power  of  research  of  hith- 
erto unapproachable  delicacy,  by  which  new  elements  have 
been  discovered,  and  our  knowledge  of  the  composition  of 
matter  greatly  extended  and  refined.  And,  what  is  much 
more  astonishing,  it  has  revealed  the  chemical  elements 
in  the  atmospheres  of  the  sun  and  the  stars;  and  thus 
made  chemistry  a  cosmical  instead  of  a  terrestrial  science. 
In  spectrum  analysis,  chemistry  and  physics  become  most 
intimately  united,  so  that  an  account  of  it  becomes  neces- 
sary before  closing  the  subject  of  Chemical  Physics. 

§  1.    The  lAiminous  Spectrum. 

177.  Newton's  Experiment. — The  analysis  of  the  solar 
beam  into  its  elemental  colors  by  the  prism  has  been  re- 
ferred to  in  speaking  of  the  general  properties  of  light 
(150) :  we  have  now  to  study  the  spectrum  more  carefully. 

FIG.  94. 


Kecom position  of  Light  by  a  Lens. 


Spectral  phenomena,  as  seen  in  rainbow-tints,  in  the  sparkle 
of  jewels,  the  chromatic  flashes  of  cut-glass,  and  the  gleam- 


SPECTRUM  ANALYSIS. 


ing  hues  of  clouds  at  sunset,  have  ever  been  familiar ;  But 
they  were  first  explained  by  Newton  in  his  treatise  en 
optics,  presented  to  the  Royal  Society  in  1675,  exactly 
two  hundred  years  ago.  He  showed  that  white  light,  in 
passing  through  the  prism  (Fig.  69),  is  resolved  into  its 
elements,  forming  a  splendid  colored  image,  such  as  is 
shown  in  the  plate  at  the  beginning  of  the  volume.  This 
is  proved  by  reversing  the  process.  If  the  separated  col- 
ored rays  are  recombined  by  a  lens,  as  illustrated  in  Fig. 
94,  they  reproduce  the  spot  of  white  light. 

178.  The  Solar  Spectrum — The    colors   produced    by 
prismatic  analysis  are  ultimate  elements.     Those  seen  in 
the  perfect  solar  spectrum  are  in  the  highest  degree  brill- 
iant and  pure.     They  blend  with  each  other  in  impercepti- 
ble gradations,  so  that  their  number  and  limits  are  indeter- 
minate.    For  convenience  they  are  designated  as  forming 
seven  principal  groups;  but,  as  Baden  Powell  remarked, 
"  the  fact  is,  the  number  of 

primary  rays  is  not  really 
seven  but  infinite."  That 
the  colors  produced  are  in- 
capable of  further  decom- 
position may  be  showrn  by 
passing  a  beam  of  the  spec- 
trum through  a  second 
prism,  as  represented  in 
Fig.  95.  The  white  ray 
refracted  by  the  prism,  $, 
gives  the  spectrum  on  the  screen,  A  B.  Tf,  now,  an  aper- 
ture is  made  in  the  screen,  and  a  colored  pencil  passed 
through  a  second  prism,  P,  it  will  not  be  further  ana- 
lyzed, but  only  diverted  in  its  course. 

179.  Spectrum  of  the  Plectric  Light. — Any  source  of 
light  may  be  employed  to  produce  a  spectrum ;  but  next 
to  the  sun,  which  is  by  far  the  most  brilliant,  the  spec- 
trum  of  the   electric  light  is  most  powerful,  and  is  gen- 


FIG. 


Effect  of  Second  Prism. 


100 


CHEMICAL   PHYSICS. 


FIG.  96. 


erally  used  where  intense  effects  are  required.  If  two 
carbon  cylinders  (Fig.  96)  are  brought  near  each  other, 
and  the  current  of  a  powerful  vol- 
taic battery  be  sent  through  them, 
the  stream  of  discharge  takes  the  form 
of  a  brilliant  arc  of  fire  between  the 
points  with  the  emission  of  a  dazzling 
light.  This  has  to  be  inclosed  in  a 
box  or  lantern,  one  of  the  forms  of 
which  is  shown  in  Fig.  97.  As  the 
carbon-points  gradually  waste  away, 
the  distance  between  them  would  be- 
come too  great,  and  they  are  kept  in 
the  proper  position  by  the  machinery 
of  the  lamp.  The  intensity  of  the 
light  from  the  voltaic  arc  depends 


Electric  Arc 


chiefly  upon  the 
amount  of  elec- 
tricity generated, 
and  the  purity  of 
the  carbon-points. 
Measured  by  its 
chemical  effects, 
it  has  been  found 
that  the  electric 
light  from  a  Bun- 
sen  battery  of  for- 
ty-six elements 
has  nearly  one- 
fourth  the  inten- 
sity of  sunlight 
at  noon  in  Au- 
gust. The  elec- 
tric light  is  con- 
venient for  dis- 
playing the  spec- 


FIG  97. 


Klectric  Lamp. 


SPECTRUM  ANALYSIS. 


tra  produced  by  various  substances.  Fig.  96  shows  a 
piece  of  sodium  placed  for  volatilization  on  the  lower 
carbon. 

180.  Dispersion. — Although  in  prismatic  analysis  the 
colors  are  always  refracted  in  the  same  order,  yet  different 
substances  have  very  unequal  refractive  power,  and  separate 
the  rays  unequally.  The  degree  of  separation  is  called  dis- 
persion. The  dispersive  power  of  water  is  low.  A  hollow 
prism  filled  with  water  gives  a  short  spectrum,  as  shown 
in  Fig.  98  (the  lettered  lines  of  which  will  be  presently  ex- 
plained). The  dispersion  is  seen  to  be  much  greater  with 

FIG.  9b. 


Unequal  Dispersion. 

a  prism  of  crown-glass.  Again,  the  dispersive  power  of  a 
prism  of  flint-glass  is  twice  as  great  as  one  of  crown-glass : 
and  a  hollow  prism  filled  with  bisulphide  of  carbon  gives 
a  spectrum  twice  as  long  as  that  of  flint-glass.  The  denser 
the  glass  the  greater  the  dispersion ;  and  the  greater  the 
angle  in  prisms  of  all  materials,  the  greater  also  is  the 
dispersion.  But  the  spectrum  loses  in  sharpness  and  brill- 
iancy, in  proportion  as  it  is  extended. 

181.  Combination  of  Prisms. — Dispersion  may  be  in- 
creased by  adding  one  prism  to  another  in  such  a  way  that 
the  refracted  light  of  the  first  shall  pass  on  through  the 
second.  Fig.  99  shows  how  this  may  be  effected.  The 
electric  light  emerging  through  a  slit,  is  directed  by  the 
double-convex  lens  upon  a  flint-glass  prism,  and  having 


102 


CHEMICAL   PHYSICS. 


undergone  one  refraction,  falls  upon  a  second  prism  P 
filled  with  bisulphide  of  carbon,  which  then  forms  the  im- 
age V  R  upon  the  screen.  The  image  is  seen  to  be  di- 
verted more  than  90°  to  one  side.  With  a  spectrum  thus 


FIG.  99. 


Spectrum  formed  by  Two  Prisma. 

produced,  eight  feet  long,  the  colors  would  be  distinguish- 
able, but  will  have  lost  much  of  their  brilliancy. 

182.  Trains  of  Prisms.  —  For  the  usual  purposes  of 
examination,  a  single  prism  suffices  ;  but,  in  delicate  re- 
searches, it  is  often  desirable  to  increase  the  dispersion 
to  a  high  degree.  This  is  especially  the  case  in  working 
with  the  feeble  light  from  the  stars,  comets,  nebula,  and 
the  aurora.  Three,  four,  and  sometimes  a  dozen  prisms, 
are  therefore  combined  when  such  delicate  observations 
are  required  ;  and  the  whole  effect  may  be  doubled  by  re- 
flecting the  light  back  through  the  same  train,  as  will  be 
shown  when  we  come  to  speak  of  the  applications  of  the 
spectroscope  to  celestial  bodies  (204), 


SPECTRUM   ANALYSIS.  103 

§  2.   The  Spectrosco%>e. 

183,  Its  Essential  Parts. — The  spectroscope  is-  an  in- 
strument for  observing  the  spectrum.  Fig.  100  shows  its 
simplest  form,  and  the  relation  of  its  parts.  L  represents 
the  light,  winch  may  be  from  any  source,  natural  or  arti- 
ficial, the  spectrum  of  which  is  to  be  examined.  A  is  a 
tube,  closed  at  $,  but  in  the  end  of  which  there  is  a  vertical 


The  Simple  Spectroscope. 

slit,  opened  and  adjusted  by  a  slide  or  screw  (205).  This 
slit  is  a  very  important  part  of  the  instrument,  and  is 
formed  by  knife-edges  of  the  most  unchangeable  material, 
finished  with  great  accuracy,  so  as  to  give  a  perfect  line, 
though  not  more  than  ^  of  an  inch  in  thickness.  The 
light  entering  the  slit,  passes  through  a  tube  called  the 
collimator,  containing  a  lens,  by  which  the  rays  are  made 
parallel  before  falling  upon  the  prism.  The  rays  emerge 
from  the  opposite  face  of  the  prism  refracted,  yet  only 
slightly  dispersed,  so  that  the  spectrum  S  is  but  little 
larger  than  the  width  of  the  slit.  In  order  to  observe 
it  of  a  sufficient  size,  at  a  short  distance,  a  magnifying- 
glass  or  small  telescope,  F,  is  employed.  The  collima- 
tor, the  prism,  and  the  spy-glass,  are  therefore  the  es- 
sential parts;  and  in  use  the  prism  requires  to  be  covered 
to  exclude  the  interfering  light. 

184.  Measuring  the  Spectrum.— But  for  scientific  pur- 
poses the  instrument  requires  the  most  accurate  means  of 
measuring  the  spaces  of  the  spectrum.  For  this  purpose  a 
third  tube  has  been  added,  as  shown  in  Fig.  101  at  S.  At 
its  outer  end  there  is  a  glass  plate,  m,  upon  which  is  en- 


104  CHEMICAL  PHYSICS. 

graved  or  photographed  a  scale  of  minute  divisions.  A 
lamp,  JT,  throws  the  image  of  this  scale  through  the  tube 
and  lens,  so  that  it  falls  upon  the  face  of  the  prism  at  n9 
at  such  an  angle  as  to  be  reflected  by  the  polished  surface  of 
glass  through  the  telescope  Fio  the  eye.  The  scale  is  per- 
manent, and  parallel  with  it  the  observer  sees  the  spectrum 


Compound  Spectroscope. 

of  whatever  light  is  employed,  and  can  thus  fix  and  com- 
pare the  position  of  the  lines  with  exactness. 

185.  The  Mounted  Instrument. — The  foregoing  figures 
show  a  mere  skeleton  of  the  parts,  for  explanation  :  Fig. 
102  represents  the  construction  of  the  instrument  as  ready 
for  use.     A  is  the  collimator-tube,  the  slit  not  being  vis- 
ible.    A  gas-burner  is  represented  as  the  source  of  light ; 
and  a  stand  is  shown  beside  it,  with  an  arm  for  supporting 
in  the  flame   any  substances  it  is  desired  to  experiment 
with.     B  is  the  telescope  furnished  with  a  guard  to  screen 
the  eye  from  extraneous  light.      C  is  the  tube  with  the 
scale  for  measurement,   and  a  candle  for   projecting   the 
image. 

186.  Direct-Vision  Spectroscopes,— It  would  obviously 
be  an  advantage  if  the  slit,  lens,  prism,  and  telescope,  were 


SPECTRUM   ANALYSIS. 


105 


all  in  a  straight  line,  so  that  the  instrument  could  be  ap- 
plied directly  to  the  light  to  be  examined.  This  result  is 
gained  in  the  direct-vision  spectroscope.  If  two  exactly 


FKJ.  102. 


The  Common  Mounted  Spectroscope. 

similar  prisms  are  combined  in  opposite  positions,  as  in  Fig. 
103,  A  B,  the  changes  impressed  upon  a  ray  by  the  first  will 
be  counteracted  by  the  second.  But,  if  the  prisms  differ  in 
refractive  angles,  or  density  of  material,  this  counteraction 
will  not  be  complete.  The  deviation  may  be  corrected, 
which  will  give  a  straight  path  for  the  light,  but  the  dis- 
persion may  be  but  partially  corrected,  which  will  leave  a 
spectrum.  This  depends  upon  the  principle  that  the  disper- 


106 


CHEMICAL  PHYSICS. 


Fig.  103. 


Counteraction  of  Prisois. 


sive  power  of  various  kinds  of  prisms  is  not  exactly  in  the 

proportion  of  their  refractive 
power.  Hence,  if  two  crown- 
glass  prisms,  P  P  (Fig.  104), 
are  combined  with  a  flint  glass 
prism,  P',  of  greater  angle,  and 
in  a  reversed  position,  the  com- 
bination will  give  a  spectrum 
in  the  line  of  sight.  A  train 
of  prisms  thus  arranged,  and 
combined  with  a  spyglass, 

forms  the  direct-vision  spectroscope,  which  is  shown  mount- 
ed upon  a  stand,  S,  FIQ  1Q4 

in  Fig.  105.     It   may 

be  detached  from  the 

stand,    unscrewed     at 

the  centre,  and  placed 

in     a    portable    case. 

These      spectroscopes 

are    sometimes    made  straight  Course  of  Ray. 

so  small  that  they  may  be  conveniently  carried  in  the 
pocket. 

§  3.  Spectral  Lines. 

187.  Newton's  Spectrum  imperfect.— Newton  used  the 
light  from  a  round   hole  in  a  window-shutter,  so  that  his 
spectrum  consisted  of  a  series  of 
overlapping  images  of  the  aper- 
ture,   by  which    the  colors    were 
slightly  mixed.     In  this  way  the 
deeper  mysteries  of  the  spectrum 
could  not  be  disclosed ;    and  for 
g   one    hundred    and    twenty-seven 

==ssas^  _  ^  1  years  no  progress    was  made   in 

this  branch  of  knowledge.      But 
Direct- Vision  Spectroscope.        *n  1802,  Dr.  Wollaston  examined 


SPECTRUM   ANALYSIS. 


107 


the  spectrum  formed  by  a  nar- 
row opening,  and  found  that,  in- 
stead of  being  so  pure  as  was  al- 
ways supposed,  it  was  crossed  in 
various  places  by  dark  lines.  The 
discovery,  however,  although  it 
was  the  initial  step  of  modern 
spectrum  analysis,  excited  no  in- 
terest at  the  time. 

188.  Fraunhofer's  Lines. — The 
dark  lines  were  afterward  redis- 
covered, in  1814,  by  a  German 
optician  named  Fraunhofer,  who 
explored  them  so  carefully  that 
they  have  since  been  called  after 
his  name.  He  studied  the  spec- 
trum, formed  by  a  fine  slit,  with 
the  telescope,  and  found  that 
the  lines  were  very  numerous, 
that  they  varied  in  thickness  and 
were  distributed  in  unequal 
groups  through  the  spectrum.  He 
counted  590  from  the  red  to  the 
violet,  and  made  a  map  of  them 
(Fig.  106),  designating  the  most 
important  by  the  letters  of  the 
alphabet.  Fraunhofer  further 
found  that  the  lines  did  not  vary 
in  sunlight,  examined  at  differ- 
ent times ;  that  the  reflected  light 
from  the  moon,  or  from  Venus, 
gives  the  same  distribution  of 
them  as  the  sun,  while  the  spec- 
tra of  the  fixed  stars  differ  from 
those  of  the  sun,  and  from  each 
other.  From  these  considerations 


108  CHEMICAL  PHYSICS. 

Fraunhofer  drew  the  important  conclusion  that  the  cause 
of  the  dark  lines  in  the  solar  spectrum  exists  in  the  sun, 
although  what  that  cause  could  be  seemed  an  impenetra- 
ble mystery. 

189.  Dr.  Draper's  Investigations,— The  next  most  im- 
portant step,  after  Fraunhofer,  was  taken  by  Dr.  Draper, 
of  New  York.      He    was   the   first   to   use   Fraunhofer's 
spectroscope  in  this  country,  more  than  thirty  years  ago. 
He  modified  it  in  1842,  in  such  a  manner  as  to  cast  the 
fixed   lines    upon   the    sensitive    surface   of   photographic 
plates,  and  published  a  map  of  the  results,  showing  four 
great  groups  of  these  lines  beyond  the  limit  of  the  violet 
ray,  and  probably  doubling  the  number  of  lines  up  to  that 
time  known.     But,  what  is  more  important,  he  passed  to  the 
examination  of  spectra  formed  by  incandescent  terrestrial 
bodies,  and  discovered  a  principle  which  is  fundamental  in 
the  philosophy  of  the  subject.     He  determined  the  temper- 
ature  at   which   a   solid   body  begins   to   give   off  light, 
showed  that  it  is  the  same  for  all  solids ;  that,  as  the  tem- 
perature   increases,  the    colored  rays    are   emitted  in  the 
order  of  their  refrangibility,  from  red  up  to  violet;    and 
that  the  spectra  cf  all  incandescent  solids  are  continuous, 
or  without  lines  or  breaks.1 

190.  Spectra  of  Gaseous  Bodies.     But  when  a  solid  body 
is  volatilized,  its  spectrum  is  changed,  becoming   discon- 
tinuous, or  broken  up  into  separate  lines ;  and  these  are 
not  dark,  but   bright,   and  of  various  colors.      If  a  little 
sodium  is  introduced  into  the  gas-flame  (Fig.  102),  and  the 

1  As  but  very  imperfect  justice  has  been  done  to  the  work  of  Draper 
abroad,  I  am  glad  to  notice  the  following  admission  from  a  recent  and 
English  work  of  high  character :  "  It  has  been  found  that  all  solid  and 
liquid  substances  act  in  the  same  way  with  regard  to  the  increase  of  heat ; 
they  all  begin  to  be  visibly  hot  at  the  same  temperature,  and  the  spec- 
trum is  in  every  case  a  continuous  one.  This  law  was  discovered  by 
Draper  (Philosophical  Magazine,  1847).  The  only  known  exception  to 
this  law  is  glowing  solid  Erbia,  whose  spectrum  exhibits  bright  lines." — 
(Roscoe's  "  Spectrum  Analysis,"  third  edition,  p.  51.) 


SPECTRUM  ANALYSIS.  109 

spectrum  be  then  observed  through  the  telescope,  a  bright- 
yellow  line  of  light  will  appear,  always  in  the  same  po- 
sition ;  and,  if  a  higher  dispersive  power  is  applied,  this 
yellow  line  will  be  resolved  into  two,  forming  the  double 
line  which  is  the  distinguishing  spectral  mark  of  sodium.  If, 
now,  potassium  be  submitted  to  the  light,  three  lines  appear, 
two  red  at  one  extremity  of  the  spectrum,  and  a  purple  line 
at  the  other,  all  else  being  darkness.  If  electric  currents 
are  sent  through  pure  hydrogen,  oxygen,  or  nitrogen  gas, 
each  produces  a  spectrum  of  different  lines,  as  shown  in  the 
colored  frontispiece.  The  colors  of  the  lines  are  as  variable 
as  the  tints  of  the  spectrum,  and  they  vary  in  numbers 
through  an  immense  range  :  while  sodium  gives  but  two 
lines,  iron  yields  several  hundreds. 

191.  What  the  Lines  indicate.— The  spectral  lines  indi- 
cate first,  chemical  identity,  and  serve  as  tests  of  chemi- 
cal substances.     Each  element  gives  a  peculiar  spectrum, 
distinguishable  from  all  others  in  the  number,  color,  breadth, 
and  grouping  of  its  lines.     So  distinct  are  they,  that  when 
a  compound  is  vaporized  all  its  elements  are  at  once  dis- 
closed.    If  several  substances  are  volatilized  together,  all 
the  spectra  can  be  identified.     Most  of  the  lines  are  mere 
films,  like  the  finest  spider's  web,  so  that  they  really  occupy 
but  a  very  small  portion  of  the  spectrum  space.     In  some 
cases,  however,   several   of   the  bright    lines   cf  different 
bodies  seem  to  coincide ;  but  upon  narrower  scrutiny  these 
have   been   generally   found   to  show  real   though   slight 
differences  of  refrangibility.     Such  coincidences  as  are  still 
unsolved  will  probably  disappear  under  higher  instrumental 
power. 

192.  Physical  Indications. — The  spectral  lines  are  also, 
to  some  extent,  indices  of  physical  states.     With  increasing 
temperature  there  is  increasing  brilliancy  of  the  lines,  and, 
with  some  metals,  lines  come  out  under  intense  heat  that 
do  not  appear  at  lower  degrees.     Pressure  or  density  also 
affects  the  spectrum.     If  the  particles  of  a  gas  are  forced 


110  CHEMICAL  PHYSICS. 

together  so  as  to  approach  the  solid  state,  the  spectrum- 
lines  are  widened  into  band?,  so  as  to  approach  the  con- 
tinuous spectrum.  The  spectrum  of  hydrogen  may  be  thus 
made  continuous  by  great  pressure.  But  this  in  no  way 
interferes  with  the  fixity  of  the  bright  lines,  or  their  value 
as  chemical  tests. 

§  4.  Theory  of  Absorption. 

193.  What  are  the  Spectrum  Lines?— The  optical  answer 
to  this  question  is,  that  they  are  images  of  the  slit.     A 
slit  of  say  the  fiftieth  of  an  inch  would  of  course  give  on  a 
screen  a  very  fine  white  line,  which  would  be  simply  an 
image  of  the  aperture.     Now,  if  that  filmy  ribbon  of  white 
light   is    passed   through    a   prism,  the    spectrum    formed 
will  be  a  succession  of  colored  lines  into  which  the  white 
line   has  been  resolved,  and  the  whole   spectrum  will  be 
but  a  series  of  images  of  the    slit,  either  continuous   or 
broken.      It  is  easy  to  recognize  that  the   bright-colored 
lines  are  images,  but  it  may  be  asked,  what  are  the  dark 
solar  lines  images  of?     Darkness  is  absence  of  light,  and 
the  dark  lines  of  the  spectrum  simply  indicate  the  absence 
of  luminous  rays.     It  is  sometimes  supposed  that  there  are 
dark  lines  of  gossamer  delicacy  in  the  sunlight,  but  this  is 
a  misconception.     There  are  rays  wanting  in  the  sunlight, 
and  in  the  spectrum  these  vacancies  come  out  as  lines  of 
darkness.     If  the  slit  is  changed  to  a  cross,  then,  as  the 
mark  of  sodium,  we  have  a  yellow  cross,  instead  of  a  line, 
and  black  crosses  in  the  spectrum  of  sunlight. 

194,  Coincidence  of  Bright  and  Dark  Lines, — We  thus 
reach  the  vital  question  of  Spectrum  Analysis,  What  has 
become  of  the   missing  rays  of  sunlight  ?  and  what  is  the 
relation  between  the  dark  solar  lines  and  the  bright  lines 
produced  by  burning  terrestrial  substances?     That  there 
is  some  close  relation  was  suspected  by  Fraunhofer,  and 
maintained  bv  others  after  him.     The  exact  coincidence  in 


SPECTRUM  ANALYSIS. 


Ill 


position  of  the  double  dark  line  D  of  the  solar  spectrum 
and  the  double  bright  line  of  sodium  attracted  frequent  at- 
tention, and  it  was  thought  it  could  not  be  accidental. 
This  conclusion  was  at  length  reenforced  by  overwhelming 
evidence.  The  solution  of  the  problem  was  given  bv  Kirch- 


Fio.  107. 


Coincidence  of  Bright  Iron  Lines  with  Dark  Solar  Lines. 

hoff  in  1859.  In  order  to  map  the  positions  of  the  bright 
lines  of  various  metals,  he  employed  the  dark  lines  of  the 
solar  spectrum  as  his  guide.  Upon  placing  one  spectrum 
over  the  other,  he  was  astonished  to  find  that  whole  sys- 
tems of  lines  in  the  two  spectra  were  coincident  in  position 
and  gradation.  The  coincidence  of  more  than  sixty  bright 
lines  of  vaporized  iron  with  the  same  number  of  dark  solar 
lines,  the  brightest  corresponding  to  the  darkest,  was 
shown  as  represented  in  Fig.  107,  and  Kirchhoff  proved 
mathematically  that  the  chances  are  more  than  1,000,000,- 
000,000,000,000  to  1  that  this  could  not  happen  without 
some  causal  connection.  Angstrom  has  since  identified  470 
bright  iron  lines  with  the  dark  solar  lines,  and  it  has  been 
established  that  75  lines  of  calcium,  57  of  manganese,  33 
of  nickel,  and  170  of  titanium,  exactly  correspond  in  group- 
ing, breadth,  and  degree  of  shade,  with  the  same  number 
of  dark  lines  of  the  solar  spectrum, 


112  CHEMICAL   PHYSICS. 

195,  Absorption  Lines. — It  was  thus  proved  that  both 
orders  of  lines  belong  together,  and  must  have  a  common 
cause ;  but  what  is  that  cause  ?  A  step  toward  the  answer 
was  taken  by  producing  the  dark  lines  experimentally. 
When  light  is  transmitted  through  certain  vapors,  and  the* 

FIG.  108. 


Absorption  by  Vapor  of  Iodine. 

passed  through  the  prism,  the  spectra  exhibit  dark  lines, 
which  vary  in  the  different  cases.  Fig.  108  represents  the 
spectrum  thus  formed  by  the  vapor  of  iodine.  The  dark- 
lines,  in  the  lunar  band,  show  the  rays  that  have  been  in- 
tercepted, or  absorbed,  on  their  passage  through  the  vapor, 
and  they  are  hence  culled  lines  of  absorption. 

196.  What  Lines  are  absorbed? — Vapors  absorb  the 
kind  of  light  that  they  emit,  and  let  all  other  rays  pass. 
Sodium-vapor  gives  out  yellow  light,  and  so  it  stops  yellow 
light.  This  principle  is  so  important  that  we  must  show 
how  it  may  be  proved.  In  Fig.  109  suppose  the  part  ^V  G 
removed,  we  shall  then  have  the  oil-lamp  L  giving  light 
which  produces  a  continuous  spectrum,  which  is  observed 
by  the  direct-vision  spectroscope  $,  the  light  entering  at 
the  slit  s.  If  now  the  glass  tube  N'  is  interposed  (which 
is  rilled  with  hydrogen,  instead  of  air,  to  prevent  combus- 
tion), and  a  little  sodium  is  placed  in  it  and  heated  by  the 
gas-burner  6r,  the  tube  becomes  filled  with  sodium-vapor. 
Upon  now  observing  the  spectrum,  it  will  be  found  that 
th«»  red,  orange,  green,  blue,  and  violet,  have  passed  through 


SPECTRUM  ANALYSIS. 


113 


unimpaired,  while  the  yellow  is  absent,  having  been  ab- 
sorbed by  the  vapor.      If  vapors  of   lithium,  strontium, 


FIG.  109. 


Absorption  by  Sodium  Vapor. 

or  barium,  are  substituted,  the  colors  that  they  emit  when 
luminous  are  in  like  manner  extinguished. 

197.  Reversal  of  the  Lines. — The  change  from  bright  to 
dark,  or,  as  it  is  called,  "  the  reversal  of  the  spectrum,"  by 
absorption,  may  be  more  fully  shown  with  the  apparatus 
represented  in  Fig.  110.  Suppose,  again,  the  gas-burner  G 
removed,  and  a  little  sodium  placed  upon  the  carbon  of  the 
electric-lamp.  The  rays  emerging  from  the  slit  E  pass 
through  the  lens  Z,  and  the  prism  P,  and,  falling  upon  the 
large  screen,  will  give  the  yellow  line  of  sodium,  the  posi- 
tion of  which  is  marked  at  m.  When  the  sodium  has  been 
all  volatilized,  its  yellow  line  disappears,  and  there  remains 
the  continuous  spectrum  r  V.  Now  restore  the  gas-burner 
6r,  into  which  there  is  inserted  the  spoon  /,  containing  a 
bit  of  sodium,  which  soon  tinges  the  flame  yellow.  The 
lesser  screen  $,  which  allows  the  rays  to  pass  through 
its  opening,  shades  the  larger  screen  from  the  diffused 
light,  and  we  have  the  dark  line  D  exactly  in  the  position 
it  occupies  in  the  solar  spectrum.  In  the  same  way  the 
spectral  lines  of  potassium,  lithium,  strontium,  and  other 
elements,  have  been  reversed  by  absorption,  from  which  it 


114 


CHEMICAL   PHYSICS. 


is  concluded  that  the  dark  solar  lines  are  due  to  the  same 
cause,  or  are  reversed  lines.  It  is,  however,  to  be  observed 
that  these  dark  lines  are  only  relatively  dark.  The  sodium- 
vapor  in  the  experiment  continues  to  emit  its  bright  rajs, 
but  the  light  intercepted  is  so  much  more  brilliant  than 


FIG.  110 


Eeversal  of  the  Sodium  Liue. 

that  emitted  that  the  lines  appear  as  dark  spaces  in  con- 
trast with  the  adjacent  colors. 

198.  Theory  of  Absorption. — Spectrum  analysis  is  thus 
based  theoretically  upon  a  broad  principle  of  physics.  We 
have  seen  (89)  that  there  is  a  fixed  relation  between  the 
absorption  and  radiation  of  heat ;  that  is,  at  a  given  tem- 
perature, as  bodies  absorb,  so  they  radiate.  We  are  more 
familiar  with  the  principle  in  acoustics.  Resonant  bodies 
absorb  only  the  vibrations  they  can  give  out.  If  we  sing 
near  the  piano,  the  strings  sometimes  respond,  but  the  re- 
sponse is  alwa}rs  a  note  that  has  been  sung.  The  note 
sung  is  not  taken  up  by  strings  that  vibrate  differentlv. 
The  string  affected  absorbs  the  vocal  vibrations  that  strike 


SPECTRUM  ANALYSIS.  115 

them  in  one  direction,  and  emits  the  same  vibrations  in 
all  directions.  So  also  with  light  The  rays  to  which  an 
incandescent  gas  is  transparent  it  cannot  emit ;  only  those 
which  it  stops,  or  absorbs,  can  it  again  give  out.  This  is 
explained  by  the  wave-hypothesis,  on  the  principle  that 
incandescent  molecules  can  only  absorb  and  emit  undula- 
tions that  are  timed  to  their  rates  of  vibration. 

199.  Fraunhofer's  Lines  explained. — The  early  and  saga- 
cious conjecture  of  Fraunhofer  that  the  cause  of  the  dark 
solar  lines  exists  in  the  sun,  and  that  they  are  lines  of  ab- 
sorption, is  thus  verified ;  and,  moreover,  the  explanation 
that  is  forced  upon  us  gives  a  clew  to  the  constitution  of 
the  sun  itself.     The  solar  metals  must  be  in  a  volatile  state, 
which  implies   an   atmosphere   surrounding   the   sun,  and 
laden  with  metallic  vapors.     Below  this  there  must  be  a 
liquid  or  solid  nucleus  of  far  greater  heat,  the  main  source 
of  illumination,  and   that   yields  a  continuous   spectrum. 
This  is  called  the  photosphere,  or  light-giving  stratum.     As 
its  light  shines  through  the  atmosphere  above,  the  metallic 
vapors  intercept  the  rays  they  can  themselves  emit,  and 
thus  fill  the  solar  spectrum  with  dark  lines,  or  lines  of  ab- 
sorption (206,  207). 

§  5.  Spectroscopic  Applications. 

200.  Delicacy  of  the  Chemical  Indications.  —  Spectrum 
analysis  affords  a  ready,  certain,  and  delicate  means  of  test- 
ing chemical  bodies.     There  are  various  rare  metals  which 
resemble  each  other  so  closely,  that  they  are  distinguished 
with  difficulty  by  the  ordinary  methods ;  but,  however  mixed 
together,  or  with  other  substances,  when  vaporized  their 
characteristic  spectral  lines  are  detected  at  a  glance.     The 
amazing  sensitiveness   of  the   reactions  has  led   to   new 
results  which  would,  a  short  time  ago,  have  been  regarded 
as  incredible.     The  spectroscope  will  easily  detect  the  one- 
eighteen-millionth  of  a  grain  of  sodium,  and  it  has  shown 
that  sodic  chloride  (common  salt)  is  almost  omnipresent. 


116  CHEMICAL  PHYSICS. 

It  pervades  the  atmosphere  in  its  dust,  and  we  breathe  it 
in  the  air  we  inhale.  If  we  clap  our  hands,  or  shake  our 
clothing,  or  jar  the  furniture,  the  dust  set  in  motion  contains 
sodium  enough  to  affect  the  flame  and  give  its  reaction  in 
the  spectrum.  Again,  the  six-millionth  part  of  a  grain 
of  lithium  is  sufficient  to  reveal  its  beautiful  red  line,  and 
it  would  be  detected  though  mixed  with  ten  thousand 
times  its  weight  of  other  substances.  It  was  formerly 
regarded  as  a  very  rare  element,  known  to  exist  in  only 
four  minerals ;  now  it  is  found  almost  everywhere — in  the 
juices  of  plants,  fruit,  bread,  tea,  coffee,  wine,  tobacco, 
milk,  and  blood ;  also  in  meteoric  stones,  and  the  water  of 
the  Atlantic.  Dr.  Miller  found  that  the  stream  of  one 
spring  poured  out  eight  hundred  pounds  of  lithic  chloride 
everv  twenty- four  hours. 

201.  New  Elements.— That  elements  which  had  hitherto 
eluded  chemists  should  be  caught  by  the  spectrum  tests 
was  to  be  expected.     Bunsen,  in  examining  the  spectra 
of  alkalies  from  the  ashes  of  a  spring,  at  Durkheim,  noticed 
some  new  lines,  from  which  he  inferred  a  new  substance. 
He  accordingly  evaporated  forty-four  tons  of  the  water, 
and  from  its  residue  extracted  two  hundred  grains  of  what 
turned  out  to  be  the  chloride  of  a  new  metal,  which  he 
called  ccesium,  from  its  bluish-gray  spectral  line.     Three 
other  metals,  before  unknown,  and  named  Rubidium,  Thal- 
lium, and  Indium,  from  the  colors  of  their  lines,  were  sub- 
sequently found  by  the  same  means. 

202.  The  Spectroscope  in  Steel-Making. — By  what   is 
called  the  "Bessemer  process  "  cast-iron  is  changed  directly 
into  steel,  by  burning  out  its  excess  of  carbon.     A  large 
amount  of  cast-iron — five  tons  at  a  time — is  placed  in  a 
suitable  vessel,  called    a  "converter,"  where  it  is  melted, 
and  a  copious  stream  of  air  is  thrown  into  the  bottom  of 
the  vessel  by  a  powerful  blowing  apparatus.     The  atmos- 
pheric oxygen  burns  away  the  carbon  and  silicon  from  the 
molten  cast-iron,  and  the  heated  gases  issue  in  flame  at 


SPECTRUM   ANALYSIS.  117 

the  mouth  of  the  converter.  The  operation  lasts  about 
twenty  minutes,  but  it  must  be  stopped  at  a  certain  point, 
and  if  it  is  done  ten  seconds  too  early  or  too  late  the  whole 
mass  is  spoiled.  The  flame  changes  with  the  progress  of 
the  combustion,  and,  although  a  quick  and  experienced 
observer  can  judge  very  nearly  when  the  time  has  come  to 
stop  the  blast,  yet  the  spectroscope  shows  the  exact  mo- 
ment at  which  the  carbon  disappears,  and  the  combustion 
must  be  arrested. 

203.  Organic  Indications. — The  investigations  of  the 
spectra  of  organic  substances  produced  by  burning,  or  by 
the  absorptive  action  of  their  solutions,  are  already  fruit- 
ful, and  promise  to  be  of  great  future  importance.     Solu- 
tions of  blood,  magenta,  and  various  coloring-matters,  are 
identified  in  extremely  small  proportions  by  the  absorp- 
tion-bands they  produce ;    and,  by  a  combination  of  the 
spectroscope  with  the  microscope,  blood-stains  may  be  de- 
tected in  which  the  spot  contains  only  the  thousandth  of  a 
grain  of  blood,  and  is  fifty  years  old.     The  vintages  of 
wine  differ  so  considerably  in  successive  years  as  to  be  at 
first  readily  distinguished,   but  as  they  grow  old  the  dis- 
crimination becomes  difficult  and  uncertain   by   ordinary 
means.     A  skillful  English  spectroscopist,  Mr.  Sorby,  has, 
however,  shown   that,  by  this  mode  of  testing,  old  vin- 
tages can  be  as  well  identified  as  recent  ones.     Again,  this 
process  has  been   made  to  throw  light  on  physiological 
changes,  such  as  the  circulation,  and  the  rate  of  diffusion 
in  the  animal  system.     Dr.  Bence  Jones  injected  salts  of 
lithia  under  the  skins  of  Guinea-pigs,  and  then,  by  the  com- 
bustion of  the  tissues,  at  different  times,  the  appearance 
of  the  red  lithium-line  showed  the  rate  of  diffusion  of  the 
substance.     Three  grains  being  thus  injected,  in  four  min- 
utes it  was  found  to  have  made  its  way  into  the  bile  and 
the  aqueous  humors  of  the  eye,  and  in  ten  minutes  traces 
of  it  were  detected  in  the  crystalline  lens. 

204.  The  Tele-Spectroscope. — But  by  far  the  most  im- 


118  CHEMICAL  PHYSICS. 

pressive  of  all  the  applications  of  spectrum  analysis  is  to 
the  heavenly  bodies.  An  instrument  adapted  for  this  pur- 
pose, and  attached  to  the  telescope,  is  called  the  tele-spec- 
troscope. Fig.  Ill  represents  the  one  employed  by  Prof. 

FIG.  111. 


Spectroscope,  with  Train  of  Prisms. 


C.  A.  Young-,  of  Dartmouth  College,  in  his  solar  researches: 
a  a  are  clamping-rings,  which  slide  upon  a  strong  metal 
rod  firmly  fastened  to  the  telescope,  and  which  brings  the 
slit  s  of  the  instrument  exactly  in  the  focus  of  the  object- 
glass,  where  the  image  of  the  celestial  object  is  formed. 
The  light  passes  through  the  collimator  c  (about  an  inch  in 
diameter  and  ten  inches  long)  and  traverses  the  train  of 
six  prisms  p  near  their  bases.  It  is  then  twice  reflected  by 
a  rectangular  prism  r,  and  sent  back  through  the  upper  por- 
tions of  the  same  prisms,  by  which  the  effect  is  doubled. 
After  this  twelvefold  dispersion  the  rays  pass  through  the 
lesser  telescope  t,  and,  being  again  reflected  for  conven- 
ience of  observation,  are  received  by  the  eye  at  e.  The 
tangent  screw  m  serves  to  adjust  the  position  of  the 
prisms. 

205.  Viewing  a  Solar  Prominence,— Fig.  112  represents 
the  slit-plate  of  the  spectroscope,  of  its  actual  size,  the  ob- 
long bl  ick  square  being  the  slit  widely  opened  by  the 


SPECTRUM  ANALYSIS. 


119 


FIG.  112. 


screw.  This  is  brought  to  the  edge  or  limit  of  the  sun's 
image  represented  by  the  white  circular  space.  A  sun- 
spot  is  shown  near  by,  and  these 
are  often  accompanied  by  promi- 
nences. The  slit  is  shown  in  Fig. 
113  on  an  enlarged  scale.  If  the 
instrument  is  so  adjusted  as  to 
bring  the  Fraunhofer  line  C  into 
the  centre  of  the  field  of  view,  then 
on  looking  into  the  eye-piece  an 
effect  resembling  that  in  the  figure 


Opened  Slit  of  the  Spectroscope. 


FIG.  113. 


may  be  seen.  Prof.  Young  says :  "  The  red  portion  of  the 
spectrum  will  stretch  athwart  the  field  of  vision  like  a 
scarlet  ribbon  with  a  darkish  band  across  it,  and  in  that 
band  will  appear  the  prominences  like  scarlet  clouds;  so 
like  our  own  -  terrestrial  clouds,  indeed,  in 
form  and  texture,  that  the  resemblance  is 
quite  startling ;  one  might  almost  think  he 
was  looking  out  through  a  partly-opened 
door,  upon  a  sunset  sky,  except  thai  there 
is  no  variety  or  contrast  of  color;  all  the 
cloud-tints  are  of  the  same  pure  sunset 
hue." 

206.  The  Solar  Envelope. — To  the  eye  of 
c     .  science  the   sun  is  a  very  different   object 

Spectroscopic   As- 
pect of  a  Promi-   from  that  which  appears  to  common  observa- 
nence. 

tion.  The  light-giving  portion,  which  seems 
to  form  his  true  surface,  and  is  called  the  photosphere, 
while  it  incloses  the  chief  mass  of  the  sun,  is  estimated  to 
indicate  but  half  its  real  diameter,  and  but  one-seventh  of 
its  volume.  It  is  surrounded  by  a  vast,  irregular,  variable 
atmosphere,  or  envelope,  in  the  most  violent  agitation,  and 
sending  out  eruptive  masses  at  a  rate  of  motion  and  on  a 
scale  of  magnitude  that  are  almost  inconceivable.  This 
envelope  consists  of  different  parts,  which,  though  they 
can  hardly  be  regarded  as  stratified,  yet  conform  to  a  gen- 


120  CHEMICAL    PHYSICS. 

eral  order  of  position.  Lying  upon  the  photosphere  is 
what  appears  like  a  layer  of  scarlet  fire,  called  the  chromo- 
sphere, which  is  five  or  six  thousand  miles  in  thickness. 
Its  appearance,  according  to  Young,  "  is  as  if  countless 
jets  of  heated  gases  were  issuing  through  the  vents  and 
spiracles  over  the  whole  surface,  thus  clothing  it  with 
flame,  which  heaves  and  tosses  like  the  blaze  of  a  confla- 
gration." At  different  points  are  thrown  up  enormous 

FIG.  114.  FIG.  115. 


.Vertical  Eruption.— 100.000  miles  to  Filamentary  Prominence, 

the  inch. 

masses  of  gaseous  matter  to  various  elevations,  which  are 
called  prominences,  or  protuberances.  Many  hundreds  of 
them  have  been  observed  and  measured,  and  the  most  of 
them  vary  from  fifteen  to  seventy -five  thousand  miles  in 
height.  Numerous  instances  are  recorded  of  their  reach- 
ing an  elevation  of  one  hundred  thousand  miles,  and  Prof. 
Young  saw  one  over  two  hundred  thousand  miles  high. 
Their  motions  often  have  a  velocity  of  one  hundred  miles 
per  second,  and  sometimes  of  double  that  rate.  "  Their 
form  and  appearance  frequently  change  with  great  rapid- 
ity, so  that  the  motion  can  almost  be  seen  with  the  eye — 
an  interval  of  fifteen  or  twenty  minutes  being  often  suf- 
ficient to  transform,  quite  beyond  recognition,  a  mass  of 
these  flames  fifty  thousand  miles  high,  and  sometimes  em- 
bracing the  whole  period  of  their  complete  development 
or  disappearance.  Sometimes  they  consist  of  pointed 
raySj  diverging  in  all  directions,  like  hedgehog-spines. 
Sometimes  they  look  like  flames  ;  sometimes  like  sheaves 


SPECTRUM  ANALYSIS.  121 

of  grain;  sometimes  like  whirling  water-spouts,  capped 
with  a  great  cloud;  occasionally  they  present  most  ex- 
actly the  appearance  of  jets  of  liquid  fire,  rising  and  fall- 
ing in  graceful  parabolas ;  frequently  they  carry  on  their 
edges  spirals  like  the  volutes  of  an  Ionic  column ;  and  con- 


FIG.  117. 


Stemmed  Prominence.  Cyclonic  Prominence. 

tinually  they  detach  filaments  which  rise  to  a  great  eleva- 
tion, gradually  expanding  and  growing  fainter  as  they  as- 
cend, until  the  eye  loses  them." — YOUNG. 

207.  Elements  in  the  Sun. — The  principal  constituent 
of  the  chromosphere  is  hydrogen  gas,  which  is  always 
present,  as  shown  by  the  length  and  brilliancy  of  its 
spectral  lines.  The  prominences  are  regarded  as  local  ac- 
cumulations of  the  chromosphere,  which  seem  to  force 
their  way  up  from  the  interior  of  the  sun  with  great  vio- 
lence, in  the  form  of  monster  irruptions,  which  consist 
mainly  of  incandescent  hydrogen.  There  is  no  evidence 
of  oxygen,  nitrogen,  or  carbon,  in  the  sun.  Besides  hy- 
drogen, the  spectrum  reveals  the  following  solar  elements, 
as  lately  stated  by  Professor  Roscoe  : 

1.  Sodium.         5.  Iron.  9.  Zinc.  13.  Rubidium. 

2.  Calcium.        6.  Chromium.  10.  Strontium.  14.  Manganese. 

3.  Barium.         7.  Nickel.         11.  Cadmium.    15.  Aluminium. 

4.  Magnesium.  8.  Copper.        12.  Cobalt.         16.  Titanium. 


122  CHEMICAL    PHYSICS. 

These  elements  exist  in  a  condition  of  ignited  lumi- 
nous vapor,  most  abundant  in  the  lower  parts  of  the  chro- 
mosphere, but  many  of  them  are  thrown  up  to  great 
heights  in  the  prominences.  They,  no  doubt,  undergo 
condensation  by  cooling,  and  pour  back  upon  the  liquid 
photosphere  dense  sheets  of  metallic  rain.  Prcf.  Young 
states  that  sulphur  is  probably  present  in  the  'chromo- 
sphere, and  traces  of  other  elements  are  reported.  There 
are  also  solar  lines  which  correspond  to  no  known  terres- 
trial substance. 

208.  Elements  in  the  Stars. — Light  is  the  same  through- 
out the  visible  universe ;  its  nature  is  not  changed  by  the 
distances  through  which  it  travels.     In  the  case  of  the 
stars  we  have  to  deal  with  radiations,  greatly  weakened 
in  intensity,  yet,  such  is  now  the  wonderful  delicacy  of  the 
tests,  that  it  has  been  lately  proved  that  heat-rays  are  as- 
sociated  with   the  stellar  light,  and,  as  we  have  already 
seen>  the  chemical  rays,  also.     When  the  light  of  the  stars 
is  studied  by  the  spectroscope,  it  testifies,  still  further,  to 
the  physical  unity  of  the  universe,  by  showing  that  the 
same  chemical  elements  which  exist  upon  earth,  and  in  the 
sun,  are  found,  also,  in  these  distant  bodies.     In  the  spec- 
trum  of  one  star,  Aldebaran,  the  lines  of  nine  elements 
have  been  identified,  viz.,  hydrogen,  sodium,  magnesium, 
calcium,  iron,  antimony,  mercury,  bismuth,  and  tellurium — 
the  two  latter  not  having  been  found  in  the  sun.     Other 
stars  give  different  spectra  ;  many  hundreds  have  been  ob- 
served, and  hydrogen  discovered  in  all  except  two.     The 
stellar  lines  are  both  dark  and  bright,  the  former  indicating 
a  white-hot  nucleus,  sending  its  light  through  absorbing 
vapors,  and  the  latter  indicating  a  chromosphere.     Spec- 
trum analysis  thus  adds  its  powerful  evidence  to  that  al- 
ready existing,  to  show  that  the  stars  are  suns,  similar  in 
constitution  to  our  own. 

209.  A  Star  in  Conflagration. — In  May,  1866,  a  star  in 
the  constellation  of  the  "Northern  Crown,"  of  the  tenth 


SPECTRUM   ANALYSIS.  123 

magnitude,  and  so  small  as  to  be  hardly  known,  was  ob- 
served to  suddenly  blaze  out,  and  attain  an  apparent  mag- 
nitude equal  to  that  of  the  largest  stars.  Examined  by 
the  spectroscope  it  was  found  that,  in  addition  to  the  usual 
dark  lines,  there  were  the  bright  linfes  of  hydrogen,  re- 
markably clear.  The  star,  however,  soon  began  to  fade, 
and  the  bright  lines  to  dwindle,  and  after  the  lapse  of 
twelve  days,  when  it  had  fallen  to  the  eighth  magnitude, 
these  lines  had  totally  disappeared.  It  seemed  like  the 
outburst  of  prominences  upon  our  own  sun,  though  on  a 
far  more  stupendous  scale. 

210.  Marvelous  Delicacy  of  the  Investigation.— In  the 
case  of  the  sun,  the  spectroscopist  has  to  deal  with  light 
of  overpowering  brilliancy,  his  meridian  rays  being  many 
times  more  intense  than  can  be  produced  by  any  artificial 
means ;  but  the  light  of  the  stars  is  at  the  opposite  ex- 
treme. We  shall  appreciate  the  difficulty  of  these  observa- 
tions by  remembering  that  the  light  of  a  star  emanates 
from  a  mere  point — that  is,  it  has  no  sensible  magnitude, 
and  has  to  be  kept  steadily  upon  a  slit  only  the  3^  part  of 
an  inch  in  breadth,  and  which  is  constantly  altering  its  po- 
sition with  the  motion  of  the  earth.  Moreover,  this  faint 
line  of  light  has  to  be  still  further  weakened  by  being 
spread  out  into  a  band.  The  air,  besides,  is  so  unsteady 
as  to  cause  flickering,  and  confusion  of  the  spectrum.  Yet 
over  all  these  embarrassments  skill  and  patience  have 
proved  victorious.  Roscoe  says  the  spectrum  of  the  star 
Sirius  has  been  photographed  by  Huggins.  The  inten- 
sity of  the  light  of  this  star  is,  according  to  the  best 
measurements,  the  -g-.Trw.TiW.Tnnr  Part  °f  ^at  °f  ^e  sun  5 
and,  although  probably  not  less  in  size  than  sixty  of  our 
suns,  it  is  estimated  to  be  at  the  enormous  distance  of 
more  than  130,000,000,000,000  miles;  and  yet  even  this 
immense  distance  does  not  prevent  us  registering  the 
chemical  intensity  of  the  rays  which  left  Sirius  twenty- 
one  years  ago  (MILLER). 


124: 


CHEMICAL   PHYSICS. 


FIG.  118. 


The  Two  Solar  Spectra. 


211.  The  Double  Solar  Spectrum. — Another  remarkable 
result  remains  to  be  noticed,  the  spectroscopic  proof  of  the 
motions  of  celestial  masses ;  and  to  explain  this  we  must 
refer  again  to  the  sun.     As  from  his  photosphere  we  get 
dark  lines,  and  frofn  his  chromosphere  bright  ones,  how  are 
they  related  to  each   other  ?      The  lines   from   the  same 
elements  having    the  same   positions,   if   the   bright  and 
dark  spectra  are  brought  together  they  should  be  continu- 
ous, and  such  is  the  fact.     If 
the  spectroscope  be  placed  ra- 
dially (Fig.  118),  so  that  the 
slit  s  s  covers  the  photosphere 
p  and   the   chromosphere  c,   a 
double  spectrum  will  be  seen, 
and  the  dark  lines  will  coincide 
with  the  bright  lines.     In  Fig. 

119  the  dark  Fraunhofer  line  (7  is  continuous  with  the  scar- 
let hydrogen-line,  and  the  same  continuity  is  observed 
with  the  lines  of  other  elements. 

212.  Variations  of  the  Bright 
Solar  Lines. — It  has   been   stated 
that  the  changes   in   the    aspects 
of  the  lines  may  indicate  physical 
alterations  in  the  substances  pro- 
ducing them,  the    hydrogen-lines, 
for  example,  being  widened  when 
the  gas  is  under   pressure.      The 
bright    solar    hydrogen  -  line    H 
(Fig.  119)  is  generally  more  slen- 
der than  the  dark  line  C",  which  is 
explained  by  the  greater  rarity  of 
the  hydrogen  in  the  higher  region 
of  the  chromosphere.     At  the  base, 

however,  it  is  seen  to  be  widened,  an  effect  due  to  the 
pressure  of  the  superincumbent  mass.  But  it  is  also 
observed  that  the  bright  hydrogen-lines  are  often  bent, 


mosphere   above,  near  the  C- 
line. 


SPECTRUM  ANALYSIS. 


125 


Changes  in  the  ^-fine. 


FIG.  121. 


widened,  twisted,  and  displaced,  in  a  very  remarkable  way. 
Fig.  120  represents  F,  as  pictured  by  Lcckyer,  strongly 
bulged  and  contorted ;  and  Fig. 
121  shows  it  as  affected  by  a 
solar  cyclone.  These  alterations 
of  the  positions  of  lines,  in  the 
spectrum,  are  simply  changes  of 
refrangibility,  and,  as  the  corre- 
sponding dark  lines  suffer  no  dis- 
turbance, at  the  same  time  we  have 
to  seek  the  cause  of  the  altered  re- 
frangibility in  some  change  of  the 
hydrogen-mass  above.  An  illus- 
tration from  sound  will  help  us 
to  understand  the  cause  of  this. 
When  in  a  railway-train  we  listen  to  the  whistle  of  a 
rapidly-approaching  engine,  as  it  passes, 
the  pitch  of  the  sound  falls.  This  is  be- 
cause, with  the  advance  of  the  engine,  the 
rate  of  air- vibrations  striking  upon  the 
ear  is  increased.  In  the  same  way,  if  a 
luminous  body  is  very  rapidly  approaching 
the  eye,  the  ethereal  waves  that  enter  it 
are  increased  in  number,  and,  as  color  de- 
pends upon  their  rate,  the  pitch  of  color, 
so  to  speak,  will  be  altered.  In  the  spec" 
trum  the  effect  would  be  to  change  the  refrangibility  of  the 
rays,  and  consequently  the  position  of  the  lines.  With  the 
swift  approach  of  the  body  the  more  rapid  wave-beats 
would  displace  the  lines  toward  the  violet,  while  the  reces- 
sion of  the  body  would  shift  them  toward  the  red.  From 
this  cause  of  variation  in  the  lines,  it  becomes  possible  to 
trace  the  direction  of  gas-streams,  cvclones,  and  the  course 
of  eruptive  masses,  and  to  account  for  the  otherwise  inex- 
plicable mutations  of  the  bright  solar  line?. 

213.  Motions  of  the  Stars. — Perhaps  the  most  splendid 


The  F-line  in  a  Solar 
Cyclone. 


126  CHEMICAL   PHYSICS. 

triumph  of  spectrum  analysis  is  the  application  of  this  prin- 
ciple to  the  determinations  of  the  motions  of  the  stars. 
Hitherto  observations  have  been  limited  to  movements 
across  the  field  of  vision.  Spectrum  analysis  proves  the 
approach  and  retreat  of  the  stars  by  the  displacement  of 
the  hydrogen-lines.  Mr.  Huggins  first  established  this  by 
a  series  of  observations  upon  Sirius  of  the  most  consum- 
mate delicacy.  A  powerful  spectroscope  being  applied,  a 
slight  displacement  of  H  toward  the  red  was  discovered  arid 
verified  by  numerous  observations.  Fig.  122  shows  the  po- 
sition of  this  line  in  Sirius,  as 
violet  compared  with  its  other  deter- 
mined positions.  The  normal 
A  position  is  obtained  by  sealing 
up  pure  hydrogen  in  a  vacuum- 
is  tube,  free  from  pressure,  and 
passing  through  it  a  stream 
c  of  electric  sparks.  It  will  be 
seen  that  the  7^-line  of  Sirius  is 
started  toward  the  red,  as  com- 
.'  pared  with  both  its  normal  and 

lu.;  Celine  in  Solar  Spectrum.       ^     ^^      positk)ns,       TMs      dig. 

placement  exactly  measured  corresponds  to  a  receding  mo- 
tion of  the  star  of  twenty-nine  miles  per  second.  ^  Later 
observations  by  Mr.  Huggins,  with  instruments  of  still 
higher  power,  confirm  and  extend  these  results.  Arcturus 
is  shown  to  be  approaching  us  at  the  rate  of  fifty-five  miles 
per  second,  and  the  motions  of  various  other  stars  have 
been  established. 

Only  a  meagre  outline  of  spectrum  analysis  has  here 
been  givren,  and  it  can  convey  but  an  imperfect  idea  of  the 
extent,  precision,  and  surprising  harmony,  of  the  knowl- 
edge that  has  so  quickly  arisen  upon  this  interesting  sub- 
ject. Those  who  care  to  pursue  the  subject  further,  are 
referred  to  the  works  of  Schellen,  Roscoe,  and  Lockyer, 


PART  II. 
CHEMICAL     PRINCIPLES. 


CHAPTER  VIII. 

GENERAL    CHARACTER    OF    CHEMICAL    ACTION. 

214.  FROM  the  study  of  those  molecular  forces  which 
determine  the  forms  of  matter,  and  variously  influence  chemi- 
cal phenomena,  we  now  pass  to  the  consideration  of  chemi- 
cal changes  themselves.     There  are,  however,  certain  ele- 
mentary facts  and  principles  of  the  subject,  leading  to  im- 
portant theoretical  views,  which  it  is  necessary  to  consider 
before  stating  the  peculiar  language  of  chemistry,  or  enter- 
ing upon  the  detailed  description  of  chemical  substances. 

215.  The  Chemical  Force.— Affinity,  chemism,  or  chemi- 
cal force,  are  names  given  to  that  power  in  Nature  which 
produces  transformations  of  matter  by  altering  its  compo- 
sition.    It  acts  only  at  insensible  distances,  or  when  differ- 
ent substances  are  brought  into  the  closest  relation  with 
each  other  ;  but  its  effects  are  conspicuous,  numberless,  and 
of  the  highest  importance.     It  is  an  inherent  and  universal 
energy  of  the  natural  world,  from  which  no  form  of  matter 
is  exempt,  and  causes  incessant  and  innumerable  changes 
everywhere,  around  and  within  us.     In  the  production  of 
all  its  effects,  the  chemical  force  conforms  to  exact  and  in- 
flexible laws,  forming  a  science  equally  remarkable  for  the 
beauty  of  its  principles,  the  depth  of  its  philosophy,  and 
the  practical  value  of  its  applications. 


128  CHEMICAL  PRINCIPLES. 

216.  Elements  and  Compounds. — Chemical  force  comes 
into  play  only  between  different  kinds  of  matter.     If  there 
were  but  one  kind  of  matter  in  the  universe,  there  might 
be  physics,  but  no  chemistry;  this  science,  therefore,  deals 
with  composition,  and  implies  elements  and  compounds. 
As  the  letters  of  its  alphabet  make  up  all  the  words,  sen- 
tences, and  books  of  a  language,  so  a  small  number  of 
chemical  elements  compose  all  the  objects  of  Nature,  and 
many  thousand   artificial    compounds    made    by  chemical 
experiment.     All  chemical  changes  consist  in  producing, 
altering,   or   destroying  compounds.      The  separation  of 
compound  bodies  into  simpler  ones  is  called  decomposi- 
tion /  the  process  of  separation,  analysis.     A  highly-com- 
plex body,  like  flour,  may  be  first  separated  into  simpler 
substances,  as  gluten,  starch,  oil,  and  water,  and  this  would 
be  proximate  analysis ;  these  bodies  may  be  again  separ- 
ated into  their  final  elements,  which  is  ultimate  analysis. 
Synthesis  is  the  reverse  process,  by  which  simpler  bodies 
are  built  up  into  those  of  greater  complexity.      Qualita- 
tive analysis  determines  of   what   elements   a   compound 
consists  ;    quantitative   analysis   ascertains   their  propor- 
tions. 

217.  Characteristic  Effects  of  Chemical  Force. — It  has 
been  stated  that  the  physical  forces  alter  only  the  forms 
of  bodies,  but  do  not  affect  their  nature.     Chemism  goes 
deeper,  destroying  the  distinctive  qualities  of  substances 
and  producing  new  ones.     Newness  of  properties  in  the 
bodies  formed  is  a  consequence  of  all  chemical  action.     It 
may  convert  two  solids  into  a  liquid,  two  liquids  into  a 
solid,  or  even  two  gases  into  a  solid.     Thus,  when  black 
charcoal  and  yellow  sulphur  combine,  the  compound  formed 
is  colorless  as  water,  and   highly  volatile.     Sulphur  and 
quicksilver  unite  to  form  the  bright-red  vermilion.     Nitro- 
gen and  oxygen   are   neutral    and    tasteless,  separate  or 
mixed  ;  yet  one  of  their  compounds,  laughing-gas,  is  sweet, 
producing  delirium   when    breathed ;    and   another,  nitric 


CHARACTER   OF   CHEMICAL   ACTION.  129 

acid,  is  an  intensely  sour  corrosive  poison.  Carbon  and 
hydrogen  are  odorless,  yet  they  combine  to  produce  our 
choicest  perfumes.  Mild  and  scentless  hydrogen  and  nitro- 
gen form  the  pungent  ammonia  ;  while  suffocating  and  poi- 
sonous chlorine,  united  with  a  brilliant  metal,  gives  rise  to 
common  salt.  There  is,  however,  a  gradation  in  these 
effects.  Substances  resembling  each  other  only  lose  their 
properties  partially;  and  the  wider  their  differences,  the 
more  complete  is  the  transformation.  If  the  elements  are 
very  similar,  the  compound  will  show  its  parentage,  as,  for 
example,  in  the  union  of  metals  forming  an  alloy ;  if  quite 
unlike,  all  traces  of  its  derivation  will  be  lost. 

218.  Gradations  in  Chemical  Attraction. — When  two 
bodies  unite  to  form  a  new  substance,  the  chemical  force 
may  not  be  satisfied,  and  the  compound  may  again  unite 
with  other  substances,  forming  bodies  still  more  complex. 
But  in  such  cases  the  combining  power  is  progressively 
weakened.      Hence  highly-complex  bodies  are  generally 
less  stable  than  simpler  ones.     Thus,  for  example,  crystal- 
lized alum,  a  complex  substance,  may  be  easily  decomposed 
into  the  simpler  compounds,  water  and  burnt  alum.     The 
latter,  again,  may  be  separated  into  potassic  sulphate,  and 
aluininic  sulphate.     But  it  requires  greatly-increased  power 
to  decompose  these  into  sulphur,  potassium,  oxygen,  and 
aluminium  ;  while  no  power  hitherto  applied  has  been  suffi- 
cient to  decompose  these  substances,  and  they  are  hence 
classed  as  elements.     So  far,  only  sixty-three  of  these  sim- 
plest forms   of  .matter  have  been  brought  to  light,  most 
material  objects  being,  therefore,  compounds.     A  list  of 
the  elements  is  given  in  the  Appendix. 

219.  Conditions  of  Chemical  Action. — These  are  many 
and  various.     Such  is  the  range  of  intensities  manifested 
by  chemical  substances,  that,  while  a  mere  touch,  or  a  beam 
of  light  falling  upon  a  body,  will  sometimes  destroy  its  com- 
position, in  other  cases  decomposition  can  only  be  brought 
about  by  the  intense  and  prolonged  application  of  force. 


130  CHEMICAL  PRINCIPLES. 

220.  Influence  of  Cohesion, — As  chemical  combination 
involves  a  total  change  in  the  arrangement  of  the  internal 
parts  of  bodies,  it  is  clear  that  cohesion,  which  tends  to  hold 
'them  in  certain  fixed  positions,  must  be  opposed  to  chemi- 
cal union  ;  and,  on  the  contrary,  any  thing  which  gives  mo- 
bility to  the  particles  of  different  substances  and  enables 
them  to  approach  within  shorter  distances  of  each  other, 
must  tend  to  promote  it.     Hence  it  is  only  in  few  instances 
that  solids  combine  directly.     Their  combinations  are  fa- 
cilitated by  pulverization  and  grinding  in  mortars,  or  by 
the  aid  of  heat  or  other  forces.     Usually,  one  at  least  of 
the  combining  bodies  must  be  in  the  liquid  or  the  gaseous 
state  before  chemical  action  can  take  place. 

221.  Influence  of  Heat  and  Light. — Heat  is  a  potent 
agent  of  chemical  change  from  its  control  over  the  forms  of 
matter ;  and  so  constantly  is  it  used  in  the  laboratory  that 
the  chemist  used  to  be  called  the  "  Philosopher  by  fire." 
Sometimes  it  brings  bodies  into  conditions  favorable  for 
union,  and  then  it  may  set  up  repulsive  actions  by  which 
combination  is  overcome.     Sulphur,  in   the  melted  state, 
will  not  combine  with  carbon ;  it  must  be  converted  into 
vapor,  and  the  carbon  heated  to  redness,  before  they  can 
be  made  to  unite.     The  chemical  action  of  light  has  been 
already  considered. 

222.  Influence  of  Electricity.— Electricity  also  deter- 
mines the  combination  of  many  substances,  especially  gases, 
acting  perhaps  indirectly  by  elevation  of  temperature.     By 
passing  through  the  mixture  an  electric  spark,  the  union  of 
oxygen  with  hydrogen,  and  of  chlorine  with  hydrogen,  is 
instantaneously  brought  about.     The  voltaic  current  also, 
as  has  been  before  pointed  out  (141,  142),  is  one  of  the 
most  powerful  agenjs  of  decomposition  possessed  by  the 
chemist. 

223.  Chemical  Induction. — A  body  in  the  act  of  chemi- 
cal combination  or  decomposition  often  induces  the  same 
kind  of  activity  in  another  body,  producing  changes  in 


CHARACTER  OF  CHEMICAL  ACTION.  131 

them  by  a  kind  of  induction.  Thus  pure  copper  does  not 
dissolve  in  dilute  sulphuric  acid,  while  zinc  does.  But 
when  one  part  of  copper  is  alloyed  with  three  times  its 
weight  of  zinc,  both  metiils  pass  into  solution.  Again, 
the  compounds  of  several  metals  with  oxygen,  perfectly 
stable  by  themselves  at  ordinary  temperatures,  may  be  de- 
composed with  almost  explosive  violence  by  being  brought 
into  contact  with  a  very  unstable  compound  of  hydrogen 
and  oxygen — hydrogen  dioxide — both  compounds  being 
decomposed  together. 

224.  The  Nascent  State. — The  moment  in  which  sub- 
stances are  liberated  from  union  with  each  other  is  called 
the  nascent  (forming)  state,  and,  at  this  time,  they  often 
enter  into  combinations  which  could  not  be  formed  under 
other  circumstances.      Nitrogen   and    hydrogen  gases,  if 
mingled,  do   not   unite;    but    when   set   free   from    their 
combinations  they  readily  recombine,  at   the  moment  of 
chemical  change,  to  form  ammonia. 

225.  Catalysis. — The  chemical  union  of  bodies  is  often 
effected  or  aided  by  the  bare  presence  of  a  substance  which 
does  not  itself  undergo  any  alteration  during  the  process. 
Thus  the  presence  of  finely-divided  platinum  brings  about 
the  combination  of  oxygen  and  hydrogen  gases  at  ordinary 
temperatures,  which  would  otherwise  take  place  only  at 
red  heat.     This  is  apparently  due  to  the  power  of  finely- 
divided  and   porous  bodies  to   condense    gases   on    their 
surface,  whereby  the  atoms  of  the  combining  bodies  are 
brought  into  closer  contact.     This   form  of  chemical  in- 
duction is  termed  catalysis,  or  contact  action. 

226.  Intensities  of  Chemical  Action.— Chemical  force 
acts  through  an  infinite   range  of  intensity.     Sometimes 
the  changes  proceed  slowly,  as  in  rocks  and   soils ;  some- 
times rapidly,  as  in  growth,  decay,  or  putrefaction  ;  and 
sometimes  with  great  violence,  as  in  combustions  and  ex- 
plosions.    Our  life  depends  upon  that  quiet  rate  of  chemi- 
cal change  which  takes  place  in  breathing  or  respiration. 


132  CHEMICAL  PRINCIPLES. 

But  the  same  force  may  act  with  such  terrific  power  that  a 
few  ounces  of  nitro-glycerine  exploded  upon  the  surface 
of  a  rock  will  shatter  it  to  fragments.  That  such  forces 
may  be  dealt  with,  and  such  operations  controlled,  is  be- 
cause they  are  governed  by  inflexible  laws. 

227.  The  Mathematical  Basis  of  Chemistry,— One  of  the 
greatest  discoveries  of  modern  times  is  the  truth  that  Na- 
ture works  with  the  same  exactness  on  the  small  scale  as 
on  the  large.     It  is  the  glory  of  Newton  to  have  proved 
that  the  material  objects  of  the  universe  attract  each  other 
according  to  a  definite  mathematical  law  by  which  all  the 
celestial  and  terrestrial  motions  of  bodies  are  regulated. 
It  has  been  established  by  chemists  that  the  minutest  par- 
ticles of  matter,  in  their  actions  and  reactions,  obey  a  cor- 
responding law,  and  that  every  chemical  compound  has  a 
mathematical  constitution  as  fixed  as  that  of  the  solar  sys- 
tem itself.     The  stones  and  soil  beneath  our  feet,  and  the 
ponderous  mountains,  are  not  mere  confused  masses  of  mat- 
ter ;  they  are  pervaded  throughout  their  innermost  constitu- 
tion by  the  harmony  of  numbers.     The  fuel  we  burn  wastes 
away  before  us,  dissolves  in  air,  and  passes  beyond  the 
reach  of  sight ;  but  the  invisible  changes  among  the  un- 
seen particles  are  definite,  exact,  and  harmonious.     And 
so  it  is  with  all  chemical  mutations.     When  instruments 
of  weighing  had  attained  sufficient  perfection,  it  was  found 
that,  however  often  matter  might  change  its  form,  nothing 
was  either  gained  or  lost — that  its  quantity  remained  the 
same ;  and  it  was  soon  found.that  the  constituents  of  chemi- 
cal compounds  always  combine  in  the  same  proportions. 

228.  The  law  of  Definite  Proportions.— When, the  com- 
position of  a  sample  of  pure  water,  common  salt,  lime,  or 
any  other  substance,  is  once   accurately  determined,  the 
knowledge  applies  to  all  these  substances — their  elements 
enter  into  them   in   constant  and  invariable   proportions. 
Pure  water  consists  of  1  part  by  weight  of  hydrogen,  and 
8  parts  by  weight  of  oxygen  ;  common  salt  of  35.5  parts  of 


CHARACTER   OF   CHEMICAL  ACTION.  133 

chlorine  to  23  of  sodium.  This  principle  is  known  as  the 
law  of  definite  proportions,  and  its  consequence  is  that 
every  chemical  element  has  a  numerical  property  by  which 
it  is  governed  when  entering  into  combination.  These 
quantities  are  known  as  combining  numbers.  The  princi- 
ple holds,  moreover,  in  the  union  of  compounds  with  each 
other,  as  well  as  with  elements ;  the  combining  number  of 
a  compound  being  determined  by  adding  together  the  com- 
bining numbers  of  its  constituents. 

229.  The  Law  of  Multiple  Proportions. — The  old  idea, 
that  chemical  combination  was  indefinite,  long  held  its 
ground  against  the  gradually  accumulating  proofs  that 
all  combination  is  definite  and  constant.  But,  when  this 
principle  was  established,  it  soon  led  to  the  discovery 
of  another,  known  as  that  of  the  multiple  proportions  of 
combination.  It  was  found  that  two  elements  may  com- 
bine so  as  to  produce  several  different  substances,  and 
that  the  proportions  of  one  or  both  elements  will  be  vari- 
able in  the  different  compounds. '  But  these  variations  are 
in  simple  numerical  proportions,  each  part  being  exactly 
doubled  or  tripled  in  its  quantity.  Hence,  when  combi- 
nations occur  in  more  proportions  than  one,  the  larger 
quantities  are  multiples  of  the  smaller  by  a  whole  num- 
ber. This  principle  is  formulated  as  the  law  of  multiple 
proportions,  and  is  illustrated  by  the  following  example  of 
the  ratios  in  which  carbon  and  oxygen  unite  : 

Carbon.  Oxygen. 

Carbonic  monoxide 12         :         16 

Carbonic  dioxide 12         .         32 

The  law  is  still  more  marked  in  the  case  of  a  series 
of  compounds  of  nitrogen  and  oxygen  : 

Nitrogen.  Oxygen. 

Nitric  mon-oxide... 14  :  8 

Nitric  dioxide ...14  :         16 

Nitric  trioxide 14  :         24 

Nitric  tetraoxide 14  :         32 

Nitric  pentoxide 14  :         40 


134  CHEMICAL  PRINCIPLES. 

230.  Equivalent  Proportions. — It  results,  from  the  fore- 
going, that  the  proportions,  or  multiples  of  them,  in  which 
two  bodies  combine  with  a  third,  are  those  in  which  they 
combine  with  each  other.  For  example,  71  parts  of  chlo- 
rine unite  with  32  parts  of  sulphur,  and  with  56  parts  of 
iron;  but  32  to  56  is  the  ratio  in  which  sulphur  combines 
with  iron.  These  relative  numbers  have  been  called  equiv- 
alent proportions,  or  equivalents ;  but  this  idea  has  re- 
cently undergone  very  important  modifications,  and  an 
enlarged  and  more  accurate  conception  of  it  has  become 
the  basis  of  the  new  system  of  theoretical  chemistry  now 
to  be  considered. 


CHAPTER  IX. 

THEORETICAL     CHEMISTRY. 

§  1.   Theory  of  Atoms  and  Molecules. 

231.  The  Old  Atomic  Theory.— It  was  an  ancient  specu- 
lation that  all  matter  is  made  up  of  atoms,  or  exceedingly 
minute  particles,  which  are  endowed  with  powers  and  vir- 
tues that  explain  all  the  properties  of  things,  and  the  effects 
they   produce.     It    was  warmly  disputed    whether   these 
particles  are  capable  of  being  divided  and  subdivided  to 
infinity;  but  there  were  no  data  for  determining  this  ques- 
tion, and  the  vague  notion  of  the  atomic  constitution  of 
matter  remained  for  thousands  of  years  nothing  more  than 
an  ingenious  guess. 

232.  Dr.  Dalton  revives  it. — But,  when  science  had  ex- 
perimentally proved  that  there  are  definite  numerical  rela- 
tions among  the  minutest  parts  of  matter,  this  old  problem 
was  placed  in  a  new  light.     The  idea  of  the  definite  propor- 
tions of  chemical  combination,  at  first  strongly  resisted,  was 
established  near  the  close  of  the  last  century.     It  was  soon 


THEORETICAL   CHEMISTRY.  135 

extended  by  Dr.  Dalton,  of  Manchester,  England,  who  dis- 
covered the  law  of  multiple  proportions ;  and,  to  explain 
it,  he  went  back  to  the  old  Greek  conception  of  atoms. 
He  assumed — 1.  That  all  matter  consists  of  ultimate  and 
unchangeable  particles  or  atoms;  2.  That  atoms  of  the 
same  element  have  a  uniform  weight,  but  that  in  different 
elements  they  have  different  weights ;  3.  That  the  combin- 
ing numbers  of  chemistry  represent  these  relative  weights; 
and,  4.  That  between  these  different  atoms  there  are  attrac- 
tions, which  unite  them  by  juxtaposition  in  the  formation 
of  chemical  compounds.  Dr.  Dalton  maintained  that,  if 
these  ideas  are  accepted,  the  constancy  of  chemical  charac- 
ters and  the  definite  and  multiple  proportions  of  combina- 
tion follow  as  necessary  consequences.  This  theory  has 
been  of  great  service  in  the  modern  development  of  the 
science ;  but  it  has  been  gradually  extended  and  altered, 
until  it  now  assumes  a,  quite  different  form  from  that 
which  it  had  at  first. 

233.  The  Molecule  in  Physics. — The  extension  of  the 
atomic  theory  has  consisted  in  the  far  greater  prominence 
and  distinctness  recently  given  to  the  conception  of  the 
molecule ;  a  conception  which  has  become  fundamental,  botli 
in  physics  and  chemistry.     We  have  seen  (26,  27,  75)  that 
the  physicist  regards  all  matter  as  made  up  of  separated 
units,  with  intervening  spaces  that  allow  a  varied  freedom 
of  movement ;  and  that  upon  this  idea  is  based  the  mo- 
lecular dynamics  of  the   three   states  of  matter.     To  the 
physicist,  therefore,   molecules   are   not   abstractions,  but 
actual  things,  having  definite  magnitudes    (274),    and  he 
defines  them    as  the  smallest  particles   of  matter  which 
move  a$  units  from  state  to  state,  under  the  operation  of 
phys  ical  forces. 

234.  The  Molecule  in  Chemistry. — To  the  chemist  the 
molecule  has  also  become  no  less  a  real  thing,  but  he  views 
it  in  a  different  aspect.     The  physicist  takes  it  as  a  unit, 
and  asks  no  questions  as  to  what  it  is  made  of;  but  this  is 


}36  CHEMICAL    PRINCIPLES. 

exactly  the  question  of  the  chemist.  He  is  to  find  out 
whether  the  molecule  be  simple  or  compound,  what  kino, 
or  kinds  of  matter  it  contains,  and  what  is  its  constitution. 
The  physicist,  for  example,  grinds  a  bit  of  sugar  down  to  the 
finest  particles  of  microscopic  dust  not  the  ten-thousandth 
of  an  inch  in  diameter,  but  each  particle  still  presents  all  the 
properties  of  the  lump,  and  he  is  very  far  from  having  yet 
arrived  at  the  molecule.  He  now  puts  it  into  water  and  it 
disappears,  changing  to  the  liquid  state.  The  visible  parti- 
cle may  be  thus  divided  into  perhaps  millions  of  molecules, 
and  when  the  water  is  evaporated  the  sugar  returns  to  the 
solid  state,  with  all  its  properties  unchanged.  Again,  a  bit 
of  common  salt,  if  sufficiently  heated,  passes  into  the  state 
of  vapor,  its  molecules  being  driven  widely  asunder ;  but 
when  condensed  we  again  have  the  substance,  with  its 
characters  unaltered.  The  chemist  now  puts  the  sugar  to  a 
test  from  his  point  of  view.  He  heats  it,  or  acts  upon  it 
by  a  strong  chemical  agent,  and  finds  that  it  contains  three 
kinds  of  matter,  carbon,  oxygen,  and  hydrogen.  The  sugar 
is  destroyed,  and  the  three  new  substances  produced  from 
it  exactly  equal  it  in  weight.  The  sugar-molecule,  he  says, 
is  therefore  not  chemically  a  unit,  but  a  compound.  He 
proves  that  the  soda-molecule  is  a  compound  also,  consist- 
ing of  two  different  kinds  of  matter,  oxygen  and  sodium. 
To  the  chemist,  therefore,  the  molecule  is  not  an  ultimate 
unit,  but  a  group  of  units  of  a  still  lower  order ;  and  he 
defines  the  molecule  to  be  the  smallest  particle  of  a  sub- 
stance which  is  capable  of  existing  in  a  separate  condition, 
and  in  which  its  properties  are  preserved. 

235.  The  Atom  in  Chemistry.— The  ultimate  unit  of  the 
chemist  is  the  atom.  Molecules  and  atoms  have  hitherto 
been  confounded  together;  but  in  the  present  state  of 
chemical  science  they  represent  totally  different  things.  A 
molecule  is  a  group  of  atoms  united  by  chernism,  and  capa- 
ble of  existing  by  itself  ;  an  atom  is  the  smallest  quantity 
of  a  substance  that  can  enter  into  combination  to  produce 


THEORETICAL   CHEMISTRY  137 

the  molecule.  Atoms  are  indestructible,  molecules  sus- 
ceptible of  endless  change.  All  chemical  reactions  are 
therefore  operations  on  molecules  which  are  expressed  in 
terms  of  the  atoms  that  compose  them.  A  group  of  the 
same  kind  of  atoms  forms  an  elemental  molecule ;  a  group 
of  different  kinds  of  atoms  forms  a  compound  molecule. 
The  breaking  up  of  a  molecule  into  its  component  atoms  is 
analysis  ;  the  binding  together  of  atoms  to  form  mole- 
cules is  synthesis  ;  and  the  interchange  of  atoms  between 
different  molecules  is  known  as  metathesis. 

236.  Symbols  of  Atoms. —  The  chemical  elements  are 
represented  by  symbols  which  are  the  first  letters  of  their 
names,  and  where  different  elements  have  the  same  initial 
letter  a  small  letter  is  added,  or  the  first  letter  of  the  Latin 
synonyms.  Thus,  N  stands  for  nitrogen,  B  for  boron,  Br 
for  bromine,  and  Fe  for  iron  (ferrum). 

But  the  letter  does  not  merely  represent  the  substance ; 
it  stands  for  a  certain  quantity  of  it,  the  smallest  that  can 
enter  into  combination — the  atom.  H  not  only  symbolizes 
hydrogen,  but  one  atom  of  it,  the  weight  of  which  is  taken 
as  1.  C  stands  for  the  carbon-atom,  which  has  a  combin- 
ing weight  of  12 ;  and  O  for  the  oxygen-atom,  weighing 
16.  These  are  the  proportional  numbers  of  combination, 
and  are  also  called  atomic  numbers.  The  molecules  will, 
therefore,  be  represented  by  writing  together  the  symbols 
of  the  atoms  of  which  they  consist,  thus  :  H,  hydrogen,  and 
Cl^  chlorine,  combine  to  form  hydric  chloride,  HC1,  the  sym- 
bol of  the  molecule.  The  single  letter  always  signifies  one 
atom,  but,  if  several  atoms  are  to  be  indicated,  small  Arabic 
numerals  are  employed,  thus :  S6  means  six  atoms  of  sul- 
phur, P4  four  atoms  of  phosphorus ;  HaO  represents  the 
molecule  of  water,  and  COa  the  molecule  of  carbonic  diox- 
ide. To  represent  several  molecules  a  large  figure  is  pre- 
fixed, thus :  2HaO  indicates  two  molecules  of  water,  4CO2 
four  molecules  of  carbonic  dioxide,  and  10  (C2H6O)  ten  mol- 
ecules of  alcohol.  By  adding  together  the  atomic  weights 


138  CHEMICAL  PRINCIPLES. 

of  the  elements,  in  a  molecule,  we  get  the  molecular  weight 
Thus  for  water,  H2O,  it  is  18;  for  carbonic  dioxide,  CO2, 
it  is  44.  The  symbols  and  atomic  numbers  of  all  the  ele- 
ments are  given  in  a  table  in  the  Appendix. 

§  2.  Progress  of  Chemical  Theory. 

237.  Earlier  Views — The  progress  of  chemistry  has  con- 
sisted in  the  advance  of  theory,  that  is,  in  an  ever-widening 
view  of  facts,  and  a  deeper  insight  into  their  relations. 
The  most  ancient  theories  of  material  things  referred 
them  to  some  essential  principle,  as  air,  water,  or  fire;  and 
then,  later,  these  ideas  were  combined.  The  objects  of  Na- 
ture were  held  to  be  formed  of  various  commixtures  of 
four  elements,  fire,  air,  earth,  and  water;  and  for  mai:y 
centuries  the  properties  and  changes  of  all  substances,  ani- 
mate and  inanimate,  were  explained  on  this  hypothesis.  In 
the  seventeenth  and  eighteenth  centuries,  alchemy,  the  old 
mystical  pursuit  of  the  art  of  gold-making,  gradually  grew 
into  a  rough  science  of  experiment  by  which  much  became 
known  of  the  qualities  of  different  kinds  of  matter.  For  a 
hundred  years  the  explanation  of  chemical  changes  was 
given  by  the  theory  of  phlogiston.  This  was  held  to  be  a 
kind  of  subtile  matter,  present  in  all  combustible  bodies, 
and  absent  in  all  incombustible  bodies,  and  which  caused 
combustion-changes  by  its  escape.  The  doctrine  is  now  re- 
garded as  a  very  crude  one,  but  it  contained  truth,  and  was 
of  great  service,  in  its  time.  A  chemical  belief  that  the 
discoverer  of  oxygen,  Dr.  Priestley,  held  to  the  day  of  his 
death,  could  certainly  not  have  been  an  absurdity.  Prof. 
Cooke  has  the  following  excellent  remarks  on  this  early 
theory :  "  That  it  was  not  absurd  a  single  consideration 
will  show.  Translate  the  word  phlogiston,  energy,  and  in 
Stahl's  work  on  chemistry  and  physics,  of  1731,  put  energy 
where  he  wrote  phlogiston,  and  you  will  find  there  the 
germs  of  our  great  modern  doctrine  of  conservation  of  en- 
ergy— one  of  the  noblest  products  of  human  thought,  It 


THEORETICAL   CHEMISTRY.  139 

was  not  a  mere  fanciful  speculation  which  ruled  the  scien- 
tific thought  of  Europe  for  a  century  and  a  half.  It  was  a 
really  grand  generalization ;  but  the  generalization  was 
given  to  the  world  clothed  in  such  a  material  garb  that 
it  has  required  two  centuries  to  unwrap  the  truth." 

238.  The  Binary  Theory ;  Dualism. — With  the  abandon- 
ment of  phlogiston  as  a  ruling  principle  of  chemical  change 
the  conception  of  affinity  came  forward,  and  chemical  effects 
began  to  be  referred  to  inherent  attractions  among  different 
kinds  of  matter.     At  the  epoch  of  Lavoisier,  affinity  was 
thought  of  simply  as  a  coupling  force.     Combination  and 
decomposition  were  supposed  to  take  place  directly  among 
bodies  in  pairs ;  elements  uniting  with  elements  to  form 
binary  compounds,  and  these  uniting  again  by  twos  to  form 
double  binary  or  ternary  compounds ;  and,  when  these  were 
made  to  act  on  each  other,  the  reaction  was  represented  as 
a   double  decomposition.     This   was  known   as   the  dual 
theory,  and  was  commended  for  its  simplicity  and  strongly 
confirmed  both  by  the  beautiful  nomenclature  which  was 
adapted  to  it,  and  by  the  atomic  theory  which  followed 
soon  after.     Powerful  aid  was  also  subsequently  lent  to  it 
by  electro-chemistry.     Compounds  were  resolved  into  pairs 
by  galvanic  decomposition,  and  their  elements  were  sup- 
posed to  be  in  opposite  electrical  states,  and  to  be  united 
by  polar  forces.     In  this  system  the  controlling  idea  was 
the  properties  of  the  elements,  which  were  supposed  to  give 
character  to  compounds,  and  the  main  question  was,  What 
bodies  does  a  substance  yield  upon  analysis  ?    The  proper- 
ties of  compounds  were  referred  to  the  presence  of  pre- 
dominating constituents,  and  hence  oxygen  was  named  as 
the  acid-former,  and  hydrogen  as  the  water-former.     The 
question  as  to  how  the  constituents  of  a  compound  were 
grouped  was  hardly  raised ;  yet  it  now  turns  out  to  be  a 
question  of  very  great  importance. 

239.  Unitary  or  Substitution  Theory. — But,  as  chemical 
changes  were  more  closely  studied,  it  was  increasingly  felt 


140  CHEMICAL   PRINCIPLES. 

that  dualism,  or  mere  splitting  and  pairing,  gave  a  totally 
insufficient  account  of  them.  There  was  a  truth  in  this  idea, 
but  it  was  not  the  whole  truth.  The  conception  of  atomic 
groupings  in  a  molecule,  and  of  the  molecule  as  having 
a  unitary  constitution,  gradually  rose  into  clearness.  It 
was  found  that  the  changes  that  take  place  among  chemi- 
cal compounds  were  rather  of  the  nature  of  replacements 
and  substitutions,  which  left  the  structure  of  the  molecule 
intact.  The  constitution  of  the  molecule,  therefore,  became 
the  main  object  of  investigation.  It  was  found,  more- 
over, that  the  most  opposite  elements  could  replace  each 
other  in  a  group  without  altering  its  chemical  character. 
Chlorine,  a  powerful  electro-negative  element,  could  be  sub- 
stituted for  hydrogen,  a  strong  electro-positive  element,  in 
a  compound,  without  changing  its  characteristic  properties. 
Chemical  compounds,  instead  of  being  likened  to  magnets, 
with  a  twofold  attraction  of  opposite  poles,  were  now 
likened  rather  to  crystals  whose  angles  and  edges  may  be 
replaced  by  new  matter,  the  form  being  maintained. 

240.  Theory  of  Chemical  Types,— The  unitary  theory 
attained  fuller  expression  in  the  theory  of  types,  in  which 
molecular  structure  first  became  a  basis  of  classification. 
Most  chemical  changes  were  viewed  as  replacements,  which 
conformed  to  a  few  general  modes.  As  the  stones  of  an 
edifice  may  be  successively  exchanged,  leaving  the  style  of 
architecture  undisturbed,  so  atoms  may  replace  atoms,  leav- 
ing the  types  of  molecular  structure  unaltered.  This  im- 
portant idea  was  at  the  basis  of  the  theory.  Gerhardt 
proposed  four  such  general  types  or  patterns,  taking  hy- 
drogen, hydric  chloride,  water,  and  ammonia,  as  repre- 
sentative bodies,  and  classing  with  them  all  substances 
which  exhibit  analogous  reactions.  But  the  exceptional 
compounds  were  so  numerous  that  the  system  was  held 
to  be  inadequate  for  classification,  though  invaluable  as 
a  transition-step  to  something  broader  and  more  satisfac- 
tory. 


THEORETICAL   CHEMISTRY.  141 

§  3.   Theory  of  Atomicity  and  Quantivalence. 

241.  Variable  Combining  Capacity. — The  general  theory 
of  chemistry  now   adopted  is  the  outgrowth  of  preceding 
theories,  and  embodies  the  truths  they  have  severally  at- 
tained.    But  it  adds  an  important  principle  which  throws 
further  light  upon  chemical  operations,  and  serves  to  or- 
ganize into  a  better  system  the  later  facts  and  ideas  of 
the  science.     The  notion  of  equality  between  combining 
elements,  and  of  equivalence  among  their  atoms,  has  long 
been  fundamental  in  chemistry.     When  the  substitution 
theory  arose  it  was  still  maintained  that  the  replacements 
were,  atom  for  atom.     But  it  is  now  recognized  that  the 
replacing   power  of  different  kinds  of  atoms  is   unequal, 
through  a  very  considerable  range.     The  idea  of  variable 
combining   capacity   of   atoms   and   molecules   has   been 
worked  out  with   great  clearness,  and  is    the  distinctive 
feature  of  what  is  now  known  as  the  New  Chemistry. 

242.  Atomicity. — While  certain  kinds  of  atoms  inter- 
change with  each  other  as  true  equivalents,  atom  for  atom, 
it  is  found  that   in  other  cases  it  takes   two,  three,  or 
half  a  dozen  atoms  of  one  kind  to  equal  one  of  another 
kind  in  combining  power.     To  determine  these  degrees  of 
equivalence  of  different  bodies,  we  have  but  to  take  some 
one,  which  will  serve  as  a  measure  of  comparison  between 
them.     Hydrogen  answers  this   purpose.     It  unites  with 
chlorine,  atom  to  atom,   forming  the  molecule   of  hydric 
chloride,  HC1 ;  but  oxygen  cannot  combine  with  hydrogen 
in  this  wray;    it  must  take  two  hydrogen-atoms,  forming 
the  molecule  of  water,  H2O.     Nitrogen  again  takes  three 
atoms  of  hydrogen,    forming  the   molecule   of  ammonia, 
H3N ;  and  carbon  behaves  still  differently,  demanding  four 
hydrogen-atoms    as   in    the  molecule  of  marsh-gas,  H4C. 
We  have,  therefore,  the  four  following  molecular  construc- 
tions : 

HC1  H2O  H3N  H4C 

Hydric  Chloride.  Water.  Ammonia.  Marsh-Gas. 


142 


CHEMICAL   PRINCIPLES. 


which  vary  in  a  regular  numerical  order.  This  may 
seem  to  be  accidental,  but  it  is  not  so,  for,  if  we  take 
chlorine  instead  of  hydrogen  as  a  measure,  we  shall  get 
similar  results,  as  follows  : 

NaCl          HgCl2          SbCl3          OC14         PC16 


Sodic 
Chloride. 


Mercuric 
Chloride. 


Antimonic 
Chloride. 


Carbonic 
Chloride. 


Phosphoric 
Chloride. 


Now  this  is  not  something  that  merely  happens  among 
a  few  selected  substances;  it  illustrates  a  law  that  has 
bet  n  traced  through  the  whole  chemical  field.  It  is  ob- 
vious that  in  the  first  four  groupings,  the  elements  chlo- 
rine, oxygen,  nitrogen,  and  carbon,  can  no  longer  be  re- 
garded as  equivalents  of  each  other;  nor  are  the  sodium, 
mercury,  antimony,  carbon,  and  phosphorus,  of  the  second 
group,  equivalents  of  each  other.  Each  element  seems  to 
have  its  own  atomic  capacity.  Hydrogen,  sodium,  and 
chlorine,  go  together  in  ones ;  oxygen  and  mercury  take 
hydrogen  and  chlorine  by  twos;  nitrogen  and  antimony 
take  them  by  threes ;  carbon  takes  both  by  fours ;  and 
phosphorus  takes  its  chlorine  in  fives.  This  varying  atomic 
capacity  is  called  atomicity,  and  the  powers  of  the  differ- 
ent elements  in  this  respect  are  known  as  their  atomicities. 

243.  ftuantivalen.ee,  and  its  Expressions.  —  To  these 
chemical  relations  the  general  term  quantivalence  has  also 
been  applied ;  and  different  modes  are  employed  to  indi- 
cate the  several  atomicities  of  the  different  elements. 
They  are  as  follows  :  bodies  whose  atomic  capacity  is 

One,  are  termed  Monads,      Monatomic,      Monadic,     or     Univalent. 


Two 

Three 

Four 

Five 

Six 

Seven 


Dyads, 
Triads, 


Diatomic, 
Triatomic, 


Dyadic, 
Triadic, 


Tetrads,  Tetratomic,  Tetradic, 

Pentads,  Pentatomic,  Pentadic, 

Hexads.  Hexatomic,  Hexadic, 

Heptads,  Heptalomic,  Heptadic, 


Bivalent. 

Trivalent. 

Quadrivalent. 

Quinquivalent. 

Sexivalent. 

Septivalent. 


Bodies  with  a  higher  atomic  capacity  than  one  are  said 
to  be  polyatomic  or  multivalent.     Hydrogen,  in  the  single 


THEORETICAL   CHEMISTRY.  143 

compound  it  forms  with  chlorine,  is  assumed  as  the  stand- 
ard of  atomicity. 

Quanti valence  is  also  expressed  in  different  ways,  as 
follows : 

Monads.  Dyads.  Triads.  Tetrads.       Pentads.         Hexads. 

H1  O11  Nm  CIV  P  FeVI 

01'  S"  B"'  Si""        Bi"'"     Mn""" 

F-  Ca=          Ste  Sm  Tai         Tel 

With  the  monadic  elements  the  indices  of  atomicity 
are  generally  assumed  and  not  written. 

244.  Bonds. — To  illustrate  more  clearly  the  meaning 
and  use  of  these  indices  of  atomicity  in  representing 
chemical  combinations  and  changes,  let  us  represent  the 
atom  as  a  circle.  Its  attractions,  polarities,  or  quantiva- 
lence,  may  then  be  symbolized  by  radial  lines,  which  be- 
come the  links  of  union,  and  appear  as  follows : 

Monad.          Dyad.  Triad.         Tetrad.         Pentad.          Hexad. 


But  as  the  links  are  the  main  things,  the  circles 
(which  were  formerly  much  used)  may  be  dispensed  with, 
and  the  dashes  alone  retained  to  mark  the  quantivalence, 
thus : 

H-         -O-        VNX        -0-         >P(       )Fe< 
i  i  i 

These  links  or  dashes  are  termed  bonds.  When  chem- 
ism  takes  effect  it  is  assumed  that  the  bonds  of  different 
atoms  are  joined  together,  and  they  are  said  to  be  satisfied, 
or  closed ;  when  not  so  joined  they  are  unsatisfied,  or  free. 
The  previous  examples,  in  which  numerals  were  used, 
would  be  represented  as  follows  by  the  use  of  bonds : 

H 

H  H-O-H 

H-C1  H-O-H          H-N-H  H 

Hydric  Chloride.  Water.  Ammonia.  Marsh-Ga*. 


144  CHEMICAL  PRINCIPLES. 

ci  01-0-01      c\^9l 

Na-01       Cl-Hg-Cl       Cl-s'b-01  01  01      01 

Sodic  Mercuric  Antiraonic  Carbonic  Phosphoric 

Chloride.  Chloride.  Chloride.  Chloride.  Chloride. 

245.  The  Bonds  control  Combination.— We   have  here 
a    controlling    and     limiting    principle    of    all    chemical 
changes.     In  every  transformation  each  bond  requires  to 
be  satisfied,  and  an  atom  can  link  itself  to  others  only  to 
the  extent  of  its  bonds.     Only  those  elements  can  unite 
with  each  other,  atom  to  atom,  which  have  the  same  num- 
ber of  bonds.     "The  hydrogen, sodium, and  chlorine  atoms 
have  only  one  bond  or  pole,  and  hence,  in  combining  with 
each   other,  they  can   only  unite   in   pairs.     The  oxygen- 
atom  has  two  bonds  or  poles,  and  can  combine,  therefore, 
with  two  hydrogen-atoms,  one  at  each  pole.    The  mercury- 
atom  has  also  two  bonds,  and  takes,  in  a  similar  manner, 
two  atoms  of  chlorine;  but  it  can  only  combine  with  a 
single  atom  of  oxygen,  for  the  two  poles  of  one  just  satisfy 
the  two  poles  of  the  other.     Again,  the  atom  of  carbon 
has   four  bonds,   which  may   be   satisfied   by  either   four 
atoms  of  hydrogen,  or  four  atoms  of  chlorine,  or  two  atoms 
of  oxygen ;  or  one  atom  of  oxygen  and  two  of  chlorine ; 
or,   lastly,    one   atom    of  oxygen    and   two   of  hydrogen. 
Further,  the  atom  of  phosphorus  has  five  bonds,  and  holds 
five  atoms  of  chlorine,  or  three  atoms  of  chlorine,  and  one 
of  oxygen."     On   this    theory,  we   view    every   chemical 
compound  as  a  molecule  which  can  exist  separately  in  con- 
sequence of  the  equipoise  of  all  its  attractions,  as  shown 
by  the  closing  of  the  bonds  of  all  its  atoms. 

246.  Varying  Quantivalence  in  the  Same  Element. — Ele- 
ments are  not   limited  to  one   degree   of   quantivalence. 
Thus  nitrogen  may  act  either  as  a  triad  or  a  pentad ;  iron 
as   a  dyad,  tetrad,  or  hexad,  and  most  of  the   other  ele- 
ments may  assume  different  quantivalent  relations.     It  is 
remarkable  that  the  same  element  in  changing  its  quantiv- 


THEORETICAL   CHEMISTRY.  145 

alence  changes  its  chemical  relations  almost  as  if  it  be- 
came a  new  element,  giving  rise  to  widely  different  classes 
of  compounds  in  its  different  states  of  atomicity.  Thus 
triatomic  nitrogen  in  ammonia,  and 

H  H 

i  Hx  i 

H-N  >tf-Cl 

i  H     i 

H  H 

Ammonia  Gas.  Ammonic  Chloride. 

pentatomic  nitrogen  in  ammonic  chloride,  give  rise  to  two 
series  of  compounds,  with  a  marked  contrast  of  properties. 
Again,  manganese  unites  with  fluorine  as  a  dyad,  a  tetrad, 
and  a  hexad,  as  shown  by  the  following  graphic  symbols ; 
and  the  difference  between  the  chemical  relations  of  the 

F  F    F 

F-Mn-F  F-Mn-F 

F-Mn-F  F  F  ^F 

Mn.  Dyadic.  Mn.  Tetradic.  Mn.  Hexadic. 

diatomic  and  the  hexatomic-atom  is  said  to  be  "  almost  as 
great  as  that  between  the  atom  of  zinc  and  the  atom  of 
sulphur."  But  the  replacing  and  atom-fixing  power  of  an 
element  in  its  different  states  is  very  unequal.  Thus, 
sulphur  acts  as  a  hexad,  and  lead  as  a  tetrad ;  but  the 
most  common  condition  of  both  is  diatomic.  Nitrogen  is 
a  pentad,  but  much  more  frequently  a  triad.  Bodies  have 
thus  a  higher  and  lower  quantivalence,  and  it  has  been 
proposed  to  limit  the  term  atomicity  to  the  highest  quan- 
tivalence that  they  ever  exhibit.  But  this  is  a  less  im- 
portant property  of  an  element  than  the  leading  or  pre- 
vailing quantivalence. 

247.  Perissads  and  Artiads. — Variation  in  the  degrees 
of  quantivalence  in  an  element  is  always  dual,  that  is,  it  in- 
creases or  diminishes  by  two.  Hence,  there  are  two  series 
of  steps,  an  odd  series — one,  three,  five,  and  seven,  and  an 
even  series — two,  four,  and  six.  Elements,  whose  quan- 


146  CHEMICAL  PRINCIPLES. 

tivalence  is  odd,  are  termed  perissads ;  elements,  whose 
quantivalence  is  even,  are  called  artiads.  It  seems  to  be 
a  principle,  almost,  if  not  quite  universal,  that  an  artiad 
can  never  become  a  perissad,  nor  a  perissad  an  artiad. 
There  may  be  a  few  exceptions,  but  the  distinction  is  re- 
garded as  fundamental,  and  as  so  completely  separating 
chemical  bodies  into  two  great  divisions,  that  it  is  taken 
as  the  basis  of  present  classification. 

248.  Theory  of  Change  by  Pairs.— The  analogies  of  po- 
larity offer  an  explanation  of  the  changes  of  quantivalence 
by  pairs  of  attractions.  When  the  opposite  poles  of  a 
magnet  are  brought  together  they  neutralize  each  other ; 
and  so  it  is  thought  that  the  bonds  of  an  atom,  when  not 
closed  by  other  atoms,  may  neutralize  and  satisfy  each 
other,  in  pairs — conversely,  the  neutralized  bonds  may  be 
aroused  by  induction  of  more  strongly  polaiized  atoms 
(125).  Thus,  phosphorus  unites  with  chlorine  both  as  a 
triad  and  a  pentad  ;  and,  if  the  atoms  of  the  chlorine  mole- 
cule are  assumed  to  be  in  opposite  polar  states,  the  change 
of  Pm  to  Pv  is  explained,  thus : 


c, 
- 


T  Cl 
ci-^i-v   =   CI-P< 

01  01  01 

The  fact  that  a  single  bond  is  never  suppressed  is  thus 
accounted  for,  and  a  reason  given  why  artiads  and  pe- 
rissads  are  inconvertible.  As  the  bonds  can  only  be  satu- 
rated in  pairs,  a  pentad  can  become  a  triad  and  a  monad 
successively ;  and  a  hexad  may  be  converted  into  a  tetrad 
or  a  dyad,  as  follows : 

Perissads.  Artiads. 

, A k  , A . 


Pentad.  Triad.         Monad.  Hexad.       Tetrad.         Dyad. 


THEORETICAL   CHEMISTRY.  147 

249.  The  Free  State  of  Elements.  —  As  an  atom  or  a 
molecule  can  only  exist  separately  when  its  bonds  are  all 
closed,  that  is  when  saturated,  it  follows  that  perissads 
cannot  exist  free.     The  odd  bond  must  be  satisfied.     In 
hydrogen  gas,  therefore,  the  condition  is  not  atomic,  as  H- 
is  impossible ;  but  it  is  molecular,  or  H  -  H.     So  free  chlo- 
rine, Cl  -  Cl,  and  sodium,  Na  -  Na,  are  self-saturated  mole- 
cules.    As  the  even  bonds  of  the  artiads  can  close  each 
other,  these  elements  may  exist  as  separate  atoms ;  oxygen 
being  either  O  =  O,  or  O  >. 

250.  Importance  of  Mode  of  Linking.  —  The  quantiva- 
lence  of  a  molecule  does  not  depend  entirely  upon  the 
atomicity  of  its  elements,  but  partly  upon  the  manner  in 
which  they  are  united.     When  multivalent  atoms  are  con- 
nected together  only  by  single  bonds,  the  remaining  bonds 
will  be  free,  and  determine  the  quantivalence  of  the  group. 
Thus  the  molecule  C3H4  may   be  saturated,  or  diatomic, 
accordingly  as  two  bonds  of  the  carbon-atoms  are  disposed 
of.     This  is  seen  by  comparing  the  following  symbols : 

i 

H-C-H  ~V~ 

H-C-H  H-C-H 

Saturated.  Diatomic. 

251.  Structure  of  Molecules. — On  this  view  it  is  impos- 
sible to  avoid  the  idea  of  the  great  importance  of  the 
grouping  of  atoms  in  molecules.     If  the  relations  among 
atoms  are  such  that  they  can  be  most  accurately  repre- 
sented by  the  mechanical  conception  of  bonds  and  clamps, 
that  of  structure  in  the  molecules  inevitably  follows.    These 
structures  are  of  different  orders.     With  monads  we  can 
only  get  molecules  of  the  simplest  construction,  in  which 
the  atoms  are  paired,  as  K-C1,  H-I.     As  a  monad  has 
but  one  bond,  it  can  never  join  other  atoms  together;  but 
when  dyads  are  introduced  the  molecular  structure  becomes 
more  complex.     The  dyad  performs  a  linking  function,  and 


148  CHEMICAL  PRINCIPLES. 

in  union  with  monads  produces  molecular  chains.  Oxygen 
acts  extensively  in  this  way,  as  in 

H-O-H  H-0-Ca-O-H 

Water.  Calcic  Hydrate. 

and,  by  introducing  more  cxygen-links,  such  chains  may  be 
indefinitely  extended.  With  atoms  of  higher  quantiva- 
lence  the  complexity  is  increased  in  a  still  greater  degree, 
the  muLivalent  atom  playing  the  part  of  a  nucleus.  The 
following  scheme  represents  the  constitution  of  common 
alum  as  a  saturated  molecule  : 

O  O 

V 

O  O  O  O 

K-O-S-O-A1-A1-O-S-O-K 

ii  ii  ii 

0  O  O  O 

\  / 

s 

#  \ 

O  O 

Potassic-Aluminic  Sulphate  (Alum). 

The  double  atom  of  aluminium  is  the  nucleus  of  the 
group,  and  combines  four  subordinate  groups,  each  having 
a  nucleus  of  hexadic  sulphur.  It  matters  nothing  how 
such  a  scheme  is  drawn,  so  that  the  atomicities  are  all 
satisfied,  but  from  the  way  such  complex  molecules  break 
up  in  decomposition  it  is  inferred  that  there  must  be  some 
definite  order  of  arrangement  among  the  atoms. 

§  4.   Theory  of  Radicals. 

252.  Simple  Radicals. — The  term  radical  has  long  been 
applied  to  any  chemical  body  which  is  regarded  as  a  com- 
mon ingredient,  or  basis  of  a  series  of  compounds.  Thus 
potassium,  sulphur,  and,  in  fact,  any  element  may  be  taken 
as  the  starting-point,  or  root,  of  such  a  series.  The  sim- 
ple radicals,  or  elements,  may  be  divided  into  two  great 


THEORETICAL   CHEMISTRY.  149 

classes,  which  stand  in  opposite  relations,  the  metals  and 
the  non-metals,  the  former  being  electro-positive,  or  posi- 
tive radicals,  and  the  latter  electro-negative,  or  negative 
radicals. 

253.  Compound  Radicals. — But  it  has  been  established 
that  there  are  groups  of  elements  so  bound  together  that 
they  play  the  part  of  simple  bodies,  and  are  therefore 
called  compound  radicals  /  thus  carbon  and  nitrogen  com- 
bine to  form  the  radical  cyanogen  CN,  which  is  the  root  of 
a  series  of  compounds  much  resembling  those  formed  by 
chlorine.     Ammonium,  NH4,  is  a  compound  radical  which 
behaves  in  chemical  reactions  closely  like  the  metals,  com- 
bining  with   chlorine,    sulphur,   and   cyanogen.      Methyl, 
CH3,  is  the  radical  of  methylic  alcohol ;  and  ethyl,  CaH6,  is 
the  root  of   ethylic  alcohol,  both  of  which  are  traceable 
through  numerous  affiliated  compounds.      These  compound 
radicals  are  classed  as  positive  and  negative,  like  the  sim- 
ple ones. 

254.  Quantivalence  of  Compound  Radicals. — Compound 
radicals  also  obey  the  laws  of  quantivalence  like  simple 
radicals.     In  general  they  cannot  be  isolated,  as  they  are 
unbalanced  molecules ;  but  some  of  them  pair  with  each 
other  like  elementary  atoms,  forming  saturated  molecules 
which  can  exist  separately.  The  radical  hydroxyl,  H  -  O  -, 
cannot,  as  it   has   an   unsaturated   bond,   exist  free,  but 
coupled  as  H-O-O-H  it  forms  the  compound  known  as 
hydric  peroxide.     The  compound  radicals  interchange  with 
each  other,  and  with  the  simple  radicals,  under  the  usual 
limitations  of  atomicity,  or,  according  to  the  number  of 
free  bonds.     As  represented  by  the  graphic  symbols,  the 
following  radicals  are  monatomic : 

H    H  H  H    H 

N  H-C-  H-C    0- 

H/XH  H  H  H 

Ammonium.  Methyl.  Ethyl. 


150  CHEMICAL  PRINCIPLES. 

§  5.   Theory  of  Acids,  Bases,  and  Salts. 

255.  The  Old  View, — These  numerous   and  important 
bodies  were  long  explained  in  a  very  simple  way  on  the 
dual  theory,  already  noticed.     The  primary  elements  were 
divided  into  the  metals  and  non-metals,  which,  uniting  with 
each  other  in  pairs,  give  rise  to  binary  compounds,  acids 
and    bases.     Acids  are    sour,  corrosive    substances,  that 
turn  vegetable  blue  colors  to  red,  and  have  a  strong  chem- 
ical attraction  for  bases.     Bases,  on  the  other  hand,  are  a 
class  of  bodies,  (including  alkalies,  which  have  a  hot,  acrid 
taste,  and  restore  the  blues  discharged  by  acids,)  that  are 
marked  by  their  powerful  chemical  attraction  for  acids. 
The  union  of  acids  and  bases  gives  rise  to  the  ternary  com- 
pounds known  as  salts — bodies,  generally,  with  a  saline 
taste,  and  in  which  the  acid  and  basic  constituents  are 
partially  or  totally  neutralized.     For  example,  the  element 
oxygen,   "  the  centre  of  the  chemical  world,*'  and  long  re- 
garded as  the  acidifying  principle  of  Nature,  unites  with 
sulphur  to  form  sulphuric  acid,  SO3.     Oxygen  also  com- 
bined with  potassium  to  form  basic  potash,  KO.     These 
binaries  then  paired  in  the  production  of  the  ternary  salt, 
sulphate  of  potash,  KO,  SO3. 

Even  in  salts  affinity  is  often  not  exhausted.  They 
may  be  again  coupled,  producing  quaternary  compounds, 
or  double-salts.  Most  of  the  bodies  of  Nature  were  viewed 
as  composed  of  these  four  great  groups,  primaries,  binaries, 
ternaries,  and  quaternaries ;  and  chemistry,  for  half  a  cen- 
tury, consisted  in  extending  chemical  knowledge  under  the 
guidance  of  this  system.  But,  as  facts  have  accumulated, 
it  has  undergone  a  profound  modification. 

256.  Water  in  Relation  to  the  Theory.— Water  was  long 
supposed  to  act  only  as  a  solvent  medium,  facilitating  the 
reactions  of   other  bodies,  but  not   participating   in    the 
changes,  except  that  its  particles  were  sometimes  taken 
up,  and  appended  to  other  compounds,  as  "  water  of  hy- 


THEORETICAL   CHEMISTRY.  151 

dration,"  or  "  water  of  crystallization."  But  at  length  it 
began  to  be  recognized  that  the  elements  of  water  are 
themselves  seriously  implicated  in  the  transformations.  It 
turned  out,  in  fact,  that,  in  regard  to  the  constitution  of 
acids,  alkalies,  and  salts,  water  holds  a  controlling  relation  ; 
its  molecule  being  the  pattern  upon  which  they  are  all 
constructed.  It  was,  moreover,  found  that  the  union  of 
acids  and  bases  in  the  production  of  salts  is  not  a  direct 
combination,  or  pairing ;  but  that  acids,  bases,  and  salts, 
are  all  alike  formed  by  the  substitution  of  different  kinds 
of  atoms  for  atoms  in  the  water-group ;  the  replacements 
occurring  without  disturbing  the  type  of  the  water-mole- 
cule. The  water-group  may  be  regarded  either  as  a  mo- 
lecular chain,  with  hydrogen-atoms  at  each  end,  linked  by 
dyadic  oxygen,  H  -  O  -  H  ;  or,  as  a  compound  of  the  radi- 
cal hydroxyl  H  -  O  -,  with  hydrogen  ;  and  the  substitution 
may  be  either  for  one  hydrogen-atom,  for  the  two  hydro- 
gen-atoms, or  for  the  hydroxyl  group. 

257.  Constitutions  of  Acids. — By  comparing  the  water- 
molecule  with  acid  molecules,  the  relations  are  shown  at  a 
glance : 

Water.      H-O-H 
Hypochlorous  Acid.      H  -  O  -  Cl 

Nitric  Acid.       H-O-(NOa) 

Here  the  hydrogen  at  one  end  of  the  water-chain  has  been 
simply  replaced  by  chlorine,  and  an  acid  molecule  is  the 
result.  The  chlorine  is  a  simple  radical,  powerfully  elec- 
tro-negative, which,  by  replacing  hydrogen  in  the  water- 
molecule,  produces  an  acid.  Nitryl  (NO2)  is  a  negative 
compound  radical,  which  also  replaces  hydrogen  in  the 
water-molecule,  producing  the  powerful  nitric  acid.  An 
acid  molecule  is  therefore  one  in  which  a  negative  radical, 
simple  or  compound,  is  united  by  oxygen  to  hydrogen,  and 
it  has  the  general  formula  K  -  O  -  H . 

258.  Constitution  of  Bases. — When  pure  metallic  sodium 


152  CHEMICAL  PRINCIPLES. 

is  added  to  pure  water,  energetic  chemical  action  ensues, 
hydrogen  is  set  free,  and  the  water  becomes  alkaline  or 
basic.  If  it  is  evaporated,  a  white  powder  is  obtained, 
which  is  caustic  soda,  or  sodic  hydrate.  We  begin  with 
sodium  and  water,  and  get  sodic  hydrate  thus : 

H-O-H 
Na-O-H; 

that  is,  the  reaction  has  consisted  simply  in  the  substitu- 
tion of  Na  for  H  in  the  water-molecule,  which  has  not 
changed  its  type.  But,  as  the  sodium  is  a  diatomic  mole- 
cule, it  engages  two  molecules  of  water,  as  may  be  graphi- 
cally represented  : 

H-O-H          Na          Na-O-H          H 
H-O-H          Na          Na-O-H          H 

The  new  molecules  have  thus  exactly  the  same  struct- 
ure as  the  old.  Had  potassium  been  used,  instead  of  so- 
dium, the  reaction  would  have  been  the  same,  with  the  pro- 
duction of  another  basic  molecule.  But  sodium  and  po- 
tassium are  positive  radicals.  A  basic  molecule,  therefore, 
is  one  in  which  a  positive  radical,  simple  or  compound,  is 
united  by  oxygen  to  hydrogen,  and  its  general  formula  is 

R-O-H. 

259.  Constitution  of  Salts.— If,  now,  an  acid  molecule 
and  a  basic  molecule  are  brought  together,  a  strong  reac- 
tion takes  place  ;  but,  again,  it  is  a  substitution  that  does 
not  impair  the  molecular  type.  We  get  a  salt  which  has 

the  general  formula  R  -  O  -  R.     Thus,  an 

acid,          R-O-H)  (R-O-R      a  salt,  and 

+  c  give  < 

and  abase  R-O-H  \          (H-O-H     water. 

Compounds  in  which  a  positive  element,  or  radical,  is  linked 
to  a  negative  element  or  radical  by  oxygen,  or  some  analo- 
gous dyad,  are  termed  salts. 


THEORETICAL   CHEMISTRY.  153 

260.  Hydrates. — On  the  foregoing  view  acids  and  bases 
belong  to  the  same  class  of  compounds,  and  are  called  hy- 
drates— acid  hydrates  and  basic  hydrates.     Caustic  potash 
and  nitric  acid  are  opposite  extremes  of  the  same  series 
which  are  connected  by  bodies  of  intermediate  gradation. 
Hydrogen   is   an   essential    constituent   of   all   acids   and 
bases.     Salts  contain  no  hydrogen,  and  possess  neither 
acid  nor  basic  properties. 

261.  Quantivalence  of  Hydrates. — The  hydrogen,  which 
is  directly  linked  to  the  atomic  group  by  oxygen  in  acids, 
is  termed  basic  hydrogen ;  that  in  bases,  acid  hydrogen.    It 
is  readily  replaceable  in  the  former  case  by  other  positive 
elements  ;  in  the  latter  case  by  other  negative  elements  or 
radicals.     Hydrates  are  univalent,  bivalent,  trivalent,  etc., 
according  to  the  number  of  these  replaceable  hydrogen- 
atoms,  or  hydroxyl  groups ;  arid  acids  are  said  to  be  mono-, 
di-,  or  tri-basic;    and  bases,  mon-,  di-,  or  tri-acid,  in  the 
same  conditions. 

262.  Kinds  of  Acids  and  Bases. — Acids  or  bases  in  which 
all  the  oxygen  (or  analogous  element)  performs  a  linking 
function,  are  called  ortho-^  those  which  also  contain  oxygen 
that  is  not  linking,  are  termed  meta-,  acids  or  bases.     The 
atoms  of  ternary  molecules  may  be  connected  by  the  nega- 
tive dyads,  sulphur  and  selenium,  as  well  as  by  oxygen, 
giving  rise  to  sulphur  and  selenium  acids,  bases,  and  salts. 

263.  Classes  of  Salts.— Salts  containing  neither  acid  nor 
basic  hydrogen  are  said  to  be  normal.     Acid  salts  are 
those  which  contain  basic  hydrogen,  and  manifest  acid  re- 
actions ;  basic  salts  contain  acid  hydrogen,  and  produce 
basic  effects.     Double  salts  are   such  as  contain   two  or 
more  positive  atoms. 

264.  Anomalous  Bodies. — As   common   salt,   the    sub- 
stance which,  above  all  others,  was  long  considered  as  the 
type  of  saline  character,  contains   no  oxygen  whatever,  it 
cannot  properly  be  included  in  this  class  of  bodies.     It 
consists  of  one  atom  of  each  of  the  monad  elements,  so- 


154  CHEMICAL   PRINCIPLES. 

dium  and  chlorine,  directly  united.  Substances  of  analo- 
gous composition  have  been  called  haloids — bodies  re- 
sembling salt.  As  the  compounds  of  hydrogen  with  chlo- 
rine, and  other  elements  analogous  to  it,  likewise  contain 
no  oxygen,  though  often  termed  acids,  they  must  also  be 
excluded  from  this  group  as  above  defined.  They  are 
sometimes  distinguished  as  hydr  acids. 

265.  The  Ammonia  Type.— In  acids,  bases,  and  salts, 
the  radicals  are  linked  by  dyads,  but  triadic  elements,  as 
nitrogen,  phosphorus,  or  arsenic,-,  may  perform  a  similar 
linking  function,  and  then  we  have  a  corresponding  series 
of  bodies  on  a  new  type.  Nitrogen  is  the  nucleus  of  the 
most  important  group,  and  its  molecule  in  ammonia, 

H 

l  is  the  type  of  a  large  class  of  compounds.     If 

H  —  N  — H 

the  hydrogen  is  replaced  by  negative  radicals,  an  amide  is 
produced ;.  if  by  positive  atoms,  an  amine  results ;  if  by 
one  positive  and  one  negative  radical,  an  alkalamide  is  the 
product.  By  thus  substituting  simple  or  compound  radi- 
cals for  the  hydrogen  of  the  ammonia-molecule,  we  get  the 

H) 
derived  ammonias.      If  we  write  ammonia  as  H  >•  N,  and 

H) 

then  substitute  for  its  hydrogen  the  negative  radicals,  cyano- 
gen, iodine,  and  chlorine,  the  formation  of  the  amides  will 
be  made  clear : 

(ON)'  )  I  ) 

HkN  IVN 

H)  Hi 

Cyanamide.  Din-iodamide. 

By  replacing  the  hydrogen  with  positive  radicals,  we  get 
the  amines,  as  follows  : 

Na  )  Rb ) 

Na  f-  N  Rb  \  N 

H  )  Rb) 

Di-iodamin«.  Tri-rubidamine. 


THEORETICAL  CHEMISTRY.  155 

§  6.   Theory  of  Isomerism  and  Allotropisin. 

266.  Inorganic  Chemistry  in  Relation  to  Theory. — 
Chemical  science  has  been  long  divided  into  two  great 
branches — inorganic  chemistry,  which  treats  of  non-living 
or  mineral  substances,  and  organic  chemistry,  which  treats 
of  matter  that  composes  the  parts  of  organized  things.     In 
the  former  department  the  chemist  deals  with  all  the  ele- 
ments of  Nature  in  their  simple  physical  conditions;    in 
the  latter  he  is  occupied  with  only  a  very  few  elements  in 
circumstances  of  great  obscurity  and  complexity.     In  fact, 
organic  chemistry  was  long  regarded  as  an  impossibility, 
under  the  belief  that  the  vital  force  dominates  in  the  or- 
ganic sphere,  and  suspends  the  ordinary  laws  of  chemical 
action.     It  was  therefore  natural,  and  indeed  inevitable, 
that  inorganic  chemistry  should  be  cultivated  first,  and  that 
the  earlier  theories  of  the  science  should  be  framed  upon 
the  knowledge  obtained  by  studying  the  simpler  and  more 
general  phenomena.     Yet  the  domain  was  partial,  and  the 
knowledge    limited ;   organic  chemistry  was  a  legitimate 
and  most  important  division  of  the  science,  and  its  numer- 
ous and  remarkable  facts  being  left  out,  the  prevailing 
theories  were  necessarily  defective. 

267.  Organic  Chemistry  in  Relation  to  Theory. — But  it 
was  impossible  to  confine  the  chemists  within  these  early 
and  arbitrary  limits ;  they  pressed  into  the  organic  field, 
and  were  rewarded  by  the  discovery  of  multitudes  of  new 
substances,  many  of  them  of  great  importance.     They  also 
made  an  unexpected  conquest  by  forming,  artificially,  in 
the  laboratory,  various  compounds  which  had  hitherto  been 
regarded  as  producible  only  under  the  influence  of  life. 
Much  ingenuity  was,  however,  at  first  expended  in  the 
offort  to  bring  the  new  facts  into  harmony  with  preexisting 
theoretical  views.     The  efforts,  however,  proved  futile.     A 
new  chemistry  sprang  up  in  the  new  province,  which,  in- 
stead of  being  subordinated  to  old  theories,  powerfully  re- 


156  CHEMICAL  PRINCIPLES. 

acted  upon  them.  And  thus,  from  a  neglected  region,  long 
supposed  to  lie  beyond  the  bounds  of  the  science,  there 
came  an  influence  that  has  changed  its  whole  theoretical 
character.  The  modern  ideas  that  are  distinctive  of  the 
new  system  —  changes  by  substitution,  types,  unitary 
groups,  atomicity,  and  the  controlling  importance  of  mo- 
lecular structure — have  all  arisen  through  the  modern  in- 
vestigation of  organic  substances. 

268.  The  Organic  Elements,— Four  substances  make  up 
the  main  bulk  of  organized  bodies  throughout  the  entire 
vegetable  and  animal  kingdoms,  viz.,  hydrogen,  oxygen, 
nitrogen,  and  carbon.  The  properties  of  these  bodies  are 
remarkable.  The  three  gases  have  never  been  condensed 
to  the  liquid  or  solid  state  by  any  application  of  mechani- 
cal force,  although  they  are  constantly  reduced  to  these 
conditions  by  chemical  action.  Carbon,  on  the  other  hand, 
is  an  equally  invincible  solid,  never  having  been  liquefied 
or  vaporized  in  its  separate  state.  Hydrogen  is  the  most 
attenuated  of  bodies,  the  unit  of  the  chemical  system,  and 
the  most  widely-diffused  element  in  Nature.  Oxygen  is 
the  most  abundant  element  on  the  globe  we  inhabit,  has  an 
extreme  range  of  attractions,  and  forms  compounds  of  all 
grades  of  stabilitj'.  Nitrogen  performs  peculiar  offices  of 
the  highest  importance  in  the  world  of  life,  giving  quality 
to  the  most  complex  and  changeable  organized  compounds. 
Carbon  is  the  common  solidifying  element  in  all  organ- 
ized products,  and  by  its  peculiar  chemical  relations  stamps 
the  character  of  this  division  of  chemistry.  Hydrogen  is 
monadic,  oxygen  dyadic,  nitrogen  triadic,  and  carbon  te- 
tradic.  The  latter  element,  by  its  high  multivalence,  com- 
bines with  itself  in  interminable  series  of  radical  groups, 
which  become  the  skeletons  or  nuclei  of  a  countless  host 
of  compounds  by  linking  with  atoms  and  groups  of  other 
elements.  Organic  chemistry,  under  this  title,  has  in  fact 
now  disappeared,  and  so  important  is  the  part  played  bv 
carbon  that  this  division  of  the  subject  is  known  as  the 


THEORETICAL  CHEMISTRY.  157 

"  Chemistry  of  the  Carbon-compounds."  Prof.  Cooke,  in- 
deed, does  not  hesitate  to  say  that  "  the  number  of  known 
compounds  of  this  one  element  is  far  greater  than  those 
of  all  the  other  elements  besides." 

269.  Isomerism. — The  old  conditions  of   analytic   in- 
quiry here  obviously  failed.     It  was  not  enough  merely  to 
analyze  organic  substances,  and  state  the  elements  and  the 
proportions  of  the  elements  that  they  contained.    Analysis, 
in  fact,  now  broke  down  so  completely  as  to  leave  no  alter- 
native to  chemists  but  to  seek  the  explanation  of  the  prop- 
erties of  bodies  in  their   atomic  arrangements;  for  com- 
pounds of  the  most  diverse  properties  were  found  to  con- 
sist of  exactly  the  same  elements  in  exactly  the  same  pro- 
portions.    Butyric  acid,  an  oily  liquid,  not  easily  inflam- 
mable, which  has  the  disgusting  smell  of  rancid  butter,  and 
gives  the  acid  reaction,  has  the  formula  C4H8O2;  while 
acetic  ether,  a  limpid  liquid,  non-acid,  easily  inflammable, 
and  having  the  pleasant,  fruity  smell  of  apples,  has  also 
the  formula  C4H8O3.     These  substances  are  therefore  said 
to  be  isomeric,  a  term  meaning  equal  measure.     There  is 
no  way  of  explaining  this  difference  of  properties,  except 
on  the  theory  that  the  constituent  atoms  are  differently 
grouped  in  the  two  cases.     And  this  is  proved  by  acting 
on  the  two  molecules  with  chemical  agents,  when  they 
break  up  in  very  different  ways,  and  give  rise  to  different 
products.     Isomeric  compounds  are  often  convertible  into 
each  other  without  loss  or  addition ;  their  different  proper- 
ties must  therefore  be  ascribed,  not  to  the  presence  or 
proportions  of  certain  elements,  but  to  the  influence  of  mo- 
lecular clustering  and  structure. 

270.  Kinds  of  Isomerism. — Isomeric  phenomena  are  so 
important  that  they  have  been  discriminated  as  of  different 
kinds.     If  bodies  have  the  same  absolute  composition,  as 
in  the  example  just  quoted,  they  are  said  to  be  metameric 
compounds.     But  substances  sometimes  have  not  the  same 
atomic  composition,  although  represented  as  identical  on  a 


158  CHEMICAL  PRINCIPLES. 

percentage  scale.  They  have  only  the  same  proportions 
of  elements,  and  are  then  said  to  be  polymeric  compounds. 
Isomeric  bodies  are  called  isomerides  or  isomers. 

271.  Allotropism. — Closely  allied  to  isomerism,  in  fact, 
the  same  thing,  only  limited  to  elementary  bodies,  are  the 
phenomena  of  allotropism,  or  allotropy.     The  word  means 
different  states,  and  denotes  different  conditions,  into  which 
the  elements  are  observed  to  pass  with  the  manifestation 
of  diverse  properties.     Thus  phosphorus,  sulphur,  and  car- 
bon exist,  each  in  several  different  allotropic  forms,  with 
totally  unlike  sets  of  characters.     It  was  at  first  supposed 
that  but  few  of  the  elements  were  aliotropic,  but  it  is  now 
found  that  a  considerable  number  of  them  take  on  this 
doubleness  of  condition.     The  only  theory  of  these  effects 
hitherto  offered,  is  that  of  varying  atomic  or  molecular 
arrangement. 

§  7.   Theory  of  Combining  Volumes. 

272.  Space-Relations  of  Molecules. — It  has  been  stated 
that  the  physicist  and  the  chemist  agree  in  regarding  mole- 
cules as  actual  things,  pieces  of  matter,  amazingly  minute, 
but  just  as  real  as  planets  and  stars  are  to  the  astronomer. 
Thus  far  we  have   considered   them   only  in  relation   to 
weight ;  but  if  they  are  things  of  weight  they  must  occupy 
space,  and  have  dimensions.     Something  has  been  done 
toward  elucidating  this  problem  of  the  space-relations  of 
molecules  ;  and  physics  and  chemistry  have  both  contrib- 
uted to  the  result. 

273.  The  Law  of  Avogadro.  —  When  a  given  amount 
of  heat  is  applied  to  a  given  amount  of  matter  in  the  solid 
or  liquid  state,  the  expansions  are  unequal.     If,  for  exam- 
ple, the  same  amount  of  heat  is  applied  to  equal  volumes 
of  water,  alcohol,  and  ether,  they  expand  differently ;  but 
if   these  substances  are  converted  into  vapor,  and  then 
the  same  amount  of   heat   is   applied  to  equal  volumes, 


THEORETICAL   CHEMISTRY.  159 

a  new  result  appears :  the  vapors  now  all  expand  alike.  In 
the  change  to  the  gaseous  state  the  molecules  have  got 
free  of  each  other's  attractions,  and  enter  upon  a  common 
condition  of  mutual  repulsion.  In  this  state  all  gases  and 
vapors  obey  common  laws,  both  in  expanding  under  the 
influence  of  heat,  and  in  contracting  under  the  influence 
of  pressure.  What  can  be  the  cause  of  these  remarkable 
uniformities  ?  This  question  was  answered  by  the  Italian 
physicist,  Avogadro,  as  early  as  1811,  as  follows  :  "Equal 
volumes  of  all  substances  when  in  the  state  of  gas,  and 
under  like  conditions  of  temperature  and  pressure,  contain 
the  same  number  of  molecules"  This  is  known  as  Avo- 
gadro's  law.  The  law  of  Avogadro  cannot  be  directly 
proved,  but  it  is  indirectly  established  by  the  most  con- 
vincing evidence ;  and  it  harmonizes  and  explains  so  great 
a  number  of  physical  and  chemical  facts,  that  it  is  now 
accepted  by  both  physicists  and  chemists  as  a  fundamental 
principle. 

274.  Size  of  Molecules. — That  molecules  have  magni- 
tudes is  self-evident,  and  if  the  principle  be  true  that 
equal  numbers  occupy  equal  spaces,  it  is  inferable  that 
they  all  have  equal  magnitudes.  What  those  dimensions 
are  may  be  thought  an  impossible  problem,  and  cer- 
tainly it  must  be  one  of  great  difficulty,  and  uncertain 
results.  Yet  the  ablest  physicists  do  not  regard  its  diffi- 
culties as  insuperable,  and  claim  to  have  already  arrived  at 
approximate  conclusions  that  are  entitled  to  reasonable 
confidence.  Great  advances  have  been  made  in  recent 
times  in  minute  measurements.  Time  is  measured  in  mill- 
ionths  of  a  second,  and  lines  have  been  ruled  on  glass  plates 
numbering  224,000  to  the  inch — several  times  finer  than 
the  scale  of  wave-lengths.  From  various  lines  of  research 
of  exquisite  delicacy,  among  others,  the  relations  of  light 
to  thin  films,  the  conclusion  has  been  reached  that  the 
diameters  of  gaseous  molecules  will  not  greatly  vary  from 
the  yoT,y}rfToT  °f  an  *nc^«  According  to  a  theorem  of 


160  CHEMICAL  PRINCIPLES. 

molecular  mechanics  deduced  by  Clausius,  the  number  of 
molecules,  in  a  perfect  gas,  at  the  freezing-point,  and  with 
a  barometric  pressure  of  thirty  inches,  is  about  one  hun- 
dred thousand  million  million  million,  or  1023  to  a  cubic 
inch.  Sir  William  Thomson,  who  has  been  prominent  in 
these  investigations,  says:  "If  we  conceive  a  sphere  of 
water  as  large  as  a  pea  to  be  magnified  to  the  size  of  the 
earth,  each  molecule  being  magnified  to  the  same  extent, 
the  magnified  structure  would  be  coarser  grained  than  a 
heap  of  small  lead  shot,  but  less  coarse  grained  than  a 
heap  of  cricket-balls." 

275.  Chemical  Application  of  Avogadro's  Principle.— 
If  equal  measures  of  two  different  gases  or  vapors  contain 
the  same  number  of  molecules,  then  we  have  but  to  weigh 
these  equal  volumes  to  get  the  relative   weight  of   the 
molecules.     For  example,  a  cubic  inch  of  oxygen  weighs 
sixteen  times  as  much  as  a  cubic  inch  of  hydrogen,  under 
the  same  conditions ;  but,  if  in  every  cubic  inch  there  is 
the  same  number  of  molecules,  each  molecule  of  oxygen 
must  weigh  sixteen  times  as  much  as  each  molecule  of  hy- 
drogen.    We  have  thus  a  simple  means  of  determining 
the   molecular  weight  of  all  bodies   that  are  capable  of 
passing  into  the  aeriform  state. 

276.  The  Unit  of  Molecular  Weight— If  the  hydrogen- 
molecule  were   taken   as   the  standard,  then  the  specific 
gravity  of  any  gaseous  body  compared  with  it  would  give 
its  molecular  weight.     But  the  half-molecule  of  hydrogen 
has  been  adopted  as  the  unit,  or  1,  so  that  the  hydrogen- 
molecule  will  have  to  be  represented  by  2.     This  makes  it 
necessary  to  double  the  specific  gravities  of  gases  in  order 
to  get  the  molecular  weight.     The  volume  of  the  hydrogen- 
molecule  being  represented  by  2,  as  all  molecules  have  the 
same  volume,  they  must  also  be  represented  by  2.     As  the 
molecule  of  hydrogen  weighs  2,  the  molecule  of  oxygen, 
which  is  sixteen  times  heavier,  weighs  16  times  2,  or  32. 
The  specific  gravity  of  nitrogen,  compared  with  hydrogen, 


THEORETICAL  CHEMISTRY.  161 

is  14;  its  molecular  weight  is  therefore  28.  As  density 
is  weight  referred  to  a  unit-volume,  a  litre  of  hydrogen  is 
taken  as  the  unit  of  density  of  gases,  and  is  called  a  crith. 
The  numbers  expressing  specific  gravity  also  express  the 
density  or  weight  in  criths,  consisting  of  one  litre  of  the 
gas  or  vapor,  under  standard  conditions,  thus : 

Hydrogen.        Nitrogen.  Oxygen.  Chlorine. 

Specific  Gravity.      1  14  16  35.5 

Density.     1  crith.     14  criths.  16  criths.  35.5  criths. 

277.  Physical  Verifications. — This  method  is  of  great 
importance  in  chemical  investigations,  where  molecular 
weights  and  formula  are  to  be  determined.  Analysis, 
as  we  have  before  seen,  gives  us  only  the  proportions 
of  elements  in  a  compound.  It  tells  us,  for  example, 
that  water  consists  of  88.89  parts,  by  weight,  of  oxygen, 
and  11.11  parts  of  hydrogen,  but  this  is  only  a  ratio,  and 
may  be  expressed  as  8  to  1,  or  16  to  2,  or  24  to  3,  so  that 
the  actual  molecular  weight  of  the  water  might  be  either 
9,  18,  or  27.  But  if  now  water  is  vaporized,  and  the  vapor 
weighed,  its  density  turns  out  to  be  9  times  that  of  hy- 
drogen ;  and  this  number  multiplied  by  2  gives  18  as  the 
actual  molecular  weight  of  water.  The  molecular  weights 
of  solid  and  liquid  substances  can  only  be  chemically  ascer- 
tained by  combining  them  with  other  substances,  and  finding 
the  lowest  proportions  in  which  such  combination  ever  takes 
place,  which  is  the  molecular  weight.  Such  results  are, 
however,  indecisive,  as  new  combinations  may  give  new 
numbers.  But,  if  the  substance  is  capable  of  being  vapor- 
ized, the  indications  that  may  be  obtained  are  usually  re- 
garded as  conclusive.  It  may  here  be  stated  that  there  is 
a  kindred  closeness  in  other  numerical  relations  of  physics 
and  chemistry.  A  striking  connection  is  found  to  subsist 
between  the  atomic  weights  and  the  specific  heats  of  the 
elements,  known  as  atomic  heat.  That  is,  the  numbers  ex- 
pressing the  relative  amounts  of  heat  required  to  raise 


162 


CHEMICAL   PRINCIPLES. 


equal  weights  of  iron,  copper,  and  lead,  for  example, 
through  equal  degrees  of  temperature,  coincide  with  the 
atomic  numbers  of  these  elements.  Moreover,  the  quanti- 
ties of  electricity  expended  in  decomposing  compounds 
are  found  to  be  also  in  definite  relation  to  the  atomic 
weights  of  the  bodies  set  free. 

278.  Combining  Volumes. — Gases  combine  by  volume 
in  very  simple  ratios ;  in  some  cases  in  equal  measures 
without  condensation ;  but  if  condensation  occurs  it  is  by 
whole  units,  as  2  to  1,  3  to  1,  or  4  to  1,  as  is  illustrated  in 
the  following  cases : 


Hydrogen.  Chlorine. 


Ch 


Hydric 
loride 


Water. 


Hydrogen. 


Nitrogen. 


Carbon. 


Marsh-Gas. 


279.  Theory  of  these  Effects.— The  foregoing  ratios  of 
combining  volume  are  simple  results  of  experiment ;  but  if 
Avogadro's  law  is  assumed,  that  equal  gas-volumes  contain 
equal  numbers  of  molecules,  the  theory  of  quantivalence 
explains  the  effects.  In  the  first  case  we  have  monadic 
atoms  with  diatomic  molecules  H  -  H  and  Cl  -  Cl,  and  in 
equal  volumes  an  equal  number  of  these  molecules.  When 
the  gases  are  mingled,  the  molecules  interchange  atoms 


THE   CHEMICAL  NOMENCLATURE.  163 

producing  H  -  01  and  H  -  Cl,  but,  as  the  number  of  mole- 
cules remains  the  same,  the  volumes  remain  unaltered.  In 
the  second  case  we  have  the  dyad  oxygen,  the  molecule 
of  which  is  O=O.  Each  of  its  atoms  links  two  of  hydro- 
gen, forming  the  triatomic  molecule  H2O.  The  total  num- 
ber of  molecules  is  thus  diminished  a  third,  and  the  three 
volumes  are  consequently  reduced  to  two.  In  the  third  ex- 
ample we  have  triadic  nitrogen,  the  molecule  of  which  is 
N^N.  Each  nitrogen-atom  takes  three  hydrogen-atoms, 
forming  ammonia,  H3N.  All  the  molecules  at  first  con- 
tain two  atoms,  and  the  resulting  molecules  contain  four. 
There  is,  therefore,  but  half  the  number  of  molecules, 
and  the  four  volumes  are  reduced  to  two.  Lastly,  each 
atom  of  the  tetrad  carbon  molecule,  OC,  unites  with  four 
atoms  of  monadic  hydrogen,  and  the  resulting  molecule 
contains  five  atoms.  The  number  of  molecules  formed 
equals  the  number  of  carbon-atoms,  or  twice  the  number 
of  the  carbon-molecules,  and  hence  the  five  volumes  are 
condensed  to  two. 


CHAPTER  X. 

THE     CHEMICAL     NOMENCLATURE. 

280.  The  Science  reflected  in  its  Language. — The  terms 
used  in  chemistry  bear  the  impress  of  the  various  theoreti- 
cal stages  of  the  science.  Some  of  them,  as  gold,  silver, 
iron,  were  applied  to  substances  thousands  of  years  ago, 
before  the  science  had  taken  a  separate  form.  The  al- 
chemists were  the  first  chemists,  and  they  worked  under 
the  mystical  influence  of  astrology.  Terms  still  survive 
that  indicate  the  fancied  relations  of  substances  to  celestial 
bodies.  Quicksilver  was  associated  with  Mercury ;  silver 
with  Luna  or  the  moon  (hence  lunar  caustic) ;  and  crocus 


164  CHEMICAL   PRINCIPLES. 

Martis,  a  compound  of  iron,  is  a  vestige  of  the  old  associa- 
tion of  this  metal  with  Mars.  The  alchemists  had  a  crude 
theory  of  the  action  of  spirits  in  Nature,  and  named  vari- 
ous products  accordingly,  as  spirit  of  wine,  spirit  of  salt, 
spirit  of  hartshorn,  spirit  of  nitre,  etc.  The  first  general 
chemical  theory,  that  of  phlogiston,  gave  rise  to  a  termi- 
nology which  has  disappeared  with  the  system,  and  which 
renders  many  of  the  chemical  books  of  the  eighteenth  cen- 
tury almost  unintelligible  to  a  modern  student.  The 
system  of  naming  chemical  substances  called  the  Nomen- 
clature, which  originated  with  the  French  about  a  hundred 
years  ago,  has  been  of  immense  service,  both  in  the  ad- 
vancement and  the  diffusion  of  the  science.  When  the 
facts  of  chemistry  were  comparatively  few,  and  its  theory 
simple,  the  terminology,  which  conformed  to  the  dual  doc- 
trine, was  also  simple  and  highly  effective.  But  as  facts  of 
all  orders  rapidly  multiplied,  and  assumed  new  relations, 
the  old  system  of  expression  was  disturbed ;  and  now, 
with  the  changes  of  theor}^  the  nomenclature  has  been 
unsettled  at  various  points,  and  there  is  some  want  of 
uniformity  among  authorities  in  the  use  of  chemical  terms. 
The  main  principles,  however,  remain  in  full  force. 

281.  Naming  the  Elements. — The   names   of  the   ele- 
ments generally  given  have  been  expressive  of  some  lead- 
ing quality,  real  or  imaginary.     Thus,  oxygen,  as  has  been 
stated,  received  a  name  signifying  acid-former,  while  chlo- 
rine takes  its  name  from  its  greenish  color ;  iodine,  from  its 
purple  vapor,  and   phosphorus  from  its  being  luminous  in 
the  dark.     Analogy  of  properties   is  sometimes  indicated 
by  similarity  of  termination,  as  chlorine,  brormwe,  iodine  ; 
while  the  metals  discovered  in  modern  times  are  marked 
by  the  termination  um,  as  platinum,  thallium,  etc. 

282.  Naming   of  Compound   Radicals, — These   sub- 
stances, which,  as  we  have  seen,  are  analogous  to  elements, 
are  generally  named  from  one  or  more  of  their  constitu- 
ents, or  from  some  compound  into  which  they  enter.     The 


THE   CHEMICAL  NOMENCLATURE.  165 

terminal  syllable,  generally,  is  yl.  Thus,  the  radical  com- 
posed of  one  atom  of  hydrogen  and  one  of  oxygen  is  .called 
hydroxyl,  and  that  composed  of  one  atom  of  oxygen  and  one 
of  carbon,  carbonyl.  Ethylene  and  benzylene  are  exam- 
ples of  compound  radicals  whose  names  terminate  in  ylene. 
Exceptions  to  the  forms  given  are  found  in  the  case  of 
cyanogen,  and  in  the  numerous  compounds  formed  of 
carbon  and  hydrogen,  or  of  carbon,  oxygen,  and  hydro- 
gen, whose  names  frequently  bear  reference  to  the 
number  of  their  carbon-atoms,  as,  for  example,  trityl, 
tetryl,  etc. 

283.  Naming  of  Binary  Compounds.  —  Binary  com- 
pounds, strictly  speaking,  result  only  from  the  union  of 
two  elementary  substances,  but  the  term  is  frequently  ex- 
tended to  include  combinations  of  two  compound  radicals. 
Thus,  silicon  and  fluorine  combine  to  form  silicic-fluoride ; 
while  methyl  and  ethyl  form  methylic-ethide.  All  of  these 
compounds  are  named  by  placing  the  positive  element  Jirst, 
and  the  negative  element,  with  its  termination  changed 
to  ide,  after  it.  Thus : 


Compounds  of  Chlorine  are  called  Chlorides. 


Bromine          " 

Bromides. 

Iodine 

Iodides. 

Fluorine          " 

Fluorides. 

Sulphur           " 
Nitrogen         " 
Phosphorus    " 
Antimony        '• 

Sulphas. 
Nitrides. 
Phosphides. 
Antimom'des. 

Carbon  "         Carbonides. 


The  termination  of  the  name  of  the  positive  element  is 
changed  to  ic,  except  in  compounds,  in  which  the  positive 
element  unites  with  the  negative  element  in  variable  pro- 
portions, when  the  ending  ic  is  confined  to  the  compound 
containing  the  smaller  proportion  of  it,  while  the  termina- 


166  CHEMICAL  PRINCIPLES. 

tion  OKS  expresses  the  larger  quantity  of  the  positive  ele- 
ment.    Thus  : 

Ferrous  oxide,        FeO. 
Fem>  oxide,  Fe20a. 

Stannow  chloride,  SnCla. 
Stanm'c  chloride,     SnCl4. 

In  some  cases  the  terminations  OKS  and  ic  are  affixed 
to  the  ,ttames  of  the  elements,  as,  for  example,  in  the  well- 
known  compounds  sulphurous  and  sulphuric  oxide.  When 
the  name  of  the  positive  element  is  not  derived  from  the  Lat- 
in or  Greek  language  it  is  translated  into  the  former  be- 
fore changing  the  termination  ;  thus,  the  Latin  for  gold  is 
durum,  and  it  forms  two  compounds  with  chlorine,  one  of 
which  is  termed  aurous,  and  the  other  auric  chloride.  When 
the  number  of  compounds  formed  of  two  elements  exceeds 
two,  hypo,  under,  and  per,  over,  are  employed  to  distin- 
guish them  ;  thus,  a  compound  containing  less  oxygen 
than  chlorous  oxide  is  known  as  hypochlorous  oxide,  while 
one  containing  more  oxygen  than  chloric  oxide  would  be 
known  as  perchloric  oxide. 

284.  Prefixes. — A  system  of   naming  much   used   in 
the   following   pages    consists    in   the    use   of   numerical 
prefixes,  expressing  the    number   of  atoms    of  the   ele- 
ment.    The  compounds  of  nitrogen  and  oxygen,  all  con- 
taining two  atoms  of  nitrogen,  united  with  respectively 
one,  two,  three,  four,  and  five  atoms  of  oxygen,  are  distin- 
guished as  nitrous  monoxide,  dioxide,  trioxide,  tetroxide, 
and  pentoxide ;  while  a  compound  containing  three  atoms 
of  iron   and   four   atoms   of  oxygen   is   termed  tri-ferric- 
tetroxide.     An  exception  to  the  previous  rules  is  found 
in  compounds  consisting  of  carbon  and  hydrogen — these 
are    so  very  numerous  that  the  methods  given  cannot  be 
rigidly  applied.     The  termination  adopted  is  generally  ene. 

285.  Naming  of  Salts,  Acids,  and  Bases. — The  consti- 
tution of  these  compounds  has  been  already  explained  (257), 


THE   CHEMICAL    NOMENCLATURE.  167 

and  the  method  of  naming  them  is  a  modification  of  the 
old  system,  which  was  derived  from  the  dual  view  of 
their  constitution.  They  are  named,  like  binaries,  from 
their  constituent  atoms.  In  the  case  of  the  negative  ele- 
ment the  termination  is  changed  to  indicate  that  the  atoms 
are  linked  by  oxygen.  These  negative  terminations  are 
at 2  and  ite  /  the  positive  element  follows  the  rule  given 
(283).  Thus,  hydric  nitride  becomes,  by  the  introduction 
of  more  oxygen,  hydric  nitrate;  by  less  oxygen,  hydric 
nitrite — both  acids.  In  salts  the  element  which  replaces 
t'.ie  hydrogen  of  the  acid  becomes  the  first  term  of  the 
name.  For  example,  when  the  element  sodium  replaces 
the  hydrogen  of  hydric  nitrate,  we  obtain  sodic  nitrate ; 
when  it  replaces  the  hydrogen  of  hydric  nitrite,  we  obtain 
sodic  nitrite.  Bases  are  named  like  the  salts,  water  taking 
the  place  of  the  second  term  of  the  name.  Thus,  the  base 
which  consists  of  calcium  and  hydrogen,  linked  by  oxygen, 
is  termed  calcic  hydrate. 

The  common  names  of  the  acids  are  derived  from  those 
of  binary  compounds  containing  oxygen  by  merely  substitut- 
ing the  word  acid  for  the  word  oxide,  thus  ignoring,  in  the 
naming  of  the  compound,  the  oxygen  ;  but,  when  the  link- 
ing element  is  not  oxygen,  but  some  of  its  analogues,  a 
prefix  is  used.  Arsenic  acid  is  composed  of  arsenic  and 
hydrogen,  linked  by  oxygen ;  sulpho-arsenic  acid  of  arsenic 
and  hydrogen  linked  by  sulphur. 

286.  Naming  of  Amides,  Amines,  and  Alkalamides. — 
It  will  be  remembered  that  these  bodies  are  derived  from 
ammonia  (265)  by  replacing  one  or  more  of  the  hydrogen- 
atoms  by  other  elements  or  radicals.  They  are  named  by 
joining  the  names  of  the  substituted  elements,  either  with 
or  without  their  terminal  syllable,  with  the  termination 
amide  or  amine.  Thus,  we  have  Cyanamide,  Potassamine : 
and  the  replacing  of  more  than  one  element  or  radical  is 
indicated  by  numerical  prefixes,  thus  :  Di  iodamide,  Di-so- 
damine  ;  and,  when  these  compounds  are  derived  from  more 
8 


168  CHEMICAL  PRINCIPLES. 

than  one  molecule  of  ammonia,  the  numerical  prefix  is  in- 
serted between  the  names  of  the  elements  or  radicals  taking 
the  place  of  hydrogen  arid  the  word  amide  or  amine. 

287.  Chemical  Formula. — The  notation  and  use  of  sym- 
bols have  been  already  explained   (236).     Chemical  com- 
position and  reactions  are  expressed  by  writing  them  to- 
gether ;  and  such  written  expressions,  are  called  chemical 

i  formula.  An  empirical  formula  is  one  which  states  only 
what  substances  and  what  proportions  of  them  or  number 
of  atoms  form  a  compound  ;  a  rational  formula  aims  to  ex- 
press the  manner  of  atomic  grouping,  or  the  way  the  ele- 
ments are  combined.  The  empirical  formula  for  alcohol 
is  C2H6O,  the  rational  formula  is  C2H6.OH,  a  compound  of 
ethyl  and  hydroxyl.  When  the  atoms  of  a  group  are  more 
closely  connected  among  themselves  than  with  the  other 
constituents  of  the  compound,  or  when  they  play  the  part 
of  a  compound  radical,  they  are  separated  from  the  rest  by 
commas,  inclosed  in  a  parenthesis,  or  a  single  symbol  (Cy), 
as  in  the  case  of  cyanogen  (CaN2),  is  substituted  for  the 
group.  Thus  the  following  equation  may  be  written — 

Eg,  Catf  2  =  Hg  +  2  ON  or 
Hg  (Cy,)  =  Hg  +  2  Cy 

The  plus-sign  (  +  )  is  also  used  to  separate  atomic  groups. 

288.  Chemical  Equations. — The  results  of  chemical  re- 
action are  represented  in  the  form  of  equations,  which  de- 
pend upon  the  principle  that  nothing  is  lost  in  the  course 
of  transformation.    The  bodies  to  be  acted  upon  are  placed 
at  the  left,  and  connected    by  the  sigh  of   addition    +. 
The  sign  of  equality  =  signifies  that  the  products  of  the 
change  which  are  written  at  the  right  equal  the  bodies  at 
the  left.     The  equation  also  implies  that  the  molecules  at 
the  left  side  are  convertible  into  those  written  upon  the 
right.     The    equation    CaO  4-  H2O  =  CaO2H3    represents 
simply  that,  if  a  molecule  of  lime   be  added  to  a  mole- 
cule of  water,  the  product  formed  will  be  a  molecule  of 
calcic  hydrate  or  slacked  lime. 


PART  IIL 
DESCRIPTIVE     CHEMISTS  Y 


DIVISION  I.  — PERISSAD  ELEMENTS. 


CHAPTER    XI. 

HYDROGEN. 

Symbol,  H.     Atomic  Weight,  1 ;   Quantivalence,  1 ;  Specific  Gravity,  1 ; 
Molecular  Weight,  2  ;  Molecular  Volume,  2. 

289.  Its  Position. — In  entering  upon   the   description 
of  the  properties  of  chemical  substances  we  begin  with 
hydrogen,  which  is  taken  as  the  unit,  or  starting-point  of 
the  established  system.     It  is  an  element  of  great  impor- 
tance in  Nature,  as  well  as  in  chemical  theory ;  and  is  so 
individual  in  its  character  that  it  is  difficult  to  classify  with 
other  elements,  and  so  will  be  most  conveniently  considered 
at  first  and  by  itself. 

290.  History. — It  was   known   by  Paracelsus,  in   the 
sixteenth  century,  that  when  iron  is  dissolved  in  sulphuric 
acid  an  air  is  given  off;  this  air  was  shown  by  Boyle,  in  1672, 
to  be  inflammable ;  and  by  Lemery,  in  1700,  to  have  deto- 
nating properties.     But  the  first  exact  experiments  upon 
it  were  made  by  Cavendish  in  1766,  and  it  was  called  by 
him  inflammable  air.     In  1781  Cavendish  made  the  great 
discovery  that  water  is  the  sole  product  of  the  combustion 
of  this  gas,  and  Lavoisier  therefore   gave   it   the   name 


170 


DESCRIPTIVE   CHEMISTRY. 


hydrogen,  from  two   Greek  words   signifying  water-gen- 
erator. 

291.  Occurrence  in  Nature, — Hydrogen  is  universally 
diffused,  and  takes  an  active  and  varied  share  in  the  chemi- 
cal operations  of  Nature.  Existing  in  water,  which  is  de- 
composed with  facility,  it  pervades  the  crust  of  the  earth, 
and  ministers  to  the  transformation  of  minerals ;  while,  as 
a  large  constituent  of  all  living  things,  its  changes  con- 
tribute to  carry  on  the  processes  of  life.  It  is  present  in 
nearly  all  kinds  of  compounds,  combined  with  other  ele- 
ments. It  forms  one-ninth  of  the  weight  of  water,  and 
the  body  which  contains  the  largest  proportion  of  it  is 
hydric  carbide  (marsh-gas),  of  which  it  forms  one-fourth. 
It  was  formerly  held  that  hydrogen  does  not  exist  free  in 
Nature ;  but  it  is  now  found  uncombined  in  volcanic  gases, 
in  meteoric  stones,  and,  as  we  have  seen,  exists  free  in 
immense  masses  in  the  atmospheres  of  the  sun  and 
stars. 

f         *«* 128-  292.  Preparation.— 

Hydrogen  is  generally 
obtained  by  decompos- 
ing water  and  setting 
the  gas  free.  It  is  usu- 
ually  collected  in  in- 
verted jars  filled  with 
water,  as  represented 
in  Fig.  123.  If  a  bit 
of  the  metal  sodium 
in  a  spoon  be  placed 
under  the  mouth  of 
such  a  jar,  it  decom- 
poses the  water  rapid- 
ly, combining  with  its 
oxygen,  and  setting  free  the  hydrogen,  which  rises  in 
bubbles  and  displaces  the  water  in  the  jar.  Steam  passed 
through  a  red-hot  gun-barrel  is  decomposed  by  the  iron, 


Liberation  of  Hydrogen  by  Sodium. 


HYDROGEN.  171 

which  combines  with  the  oxygen  and  sets  the  hydrogen 
free.  A  current  of  electricity  passed  through  water  severs 
its  constituents,  and  liberates  both  oxygen  and  hydrogen, 
when  they  may  be  collected  separately  (141). 

293.  By  the  Use  of  Zinc. — Hydrogen  is  commonly  pre- 
pared, however,  by  the  action  of  dilute  hydric  sulphate  (sul- 
phuric acid)  upon  bits  of  zinc.  The  zinc  is  placed  in  a  two- 

FIG.  124. 


Preparation  of  Hydrogen. 

necked  bottle  (Fig.  124)  and  covered  with  water.  The 
tube,  with  a  funnel  at  top,  admits  the  acid,  when  the  action 
begins  at  once,  the  gas  bubbles  up  freely  and  passes  off 
through  the  curved  tube,  which  delivers  it  under  the  mouth 
of  an  inverted  jar,  as  before,  but  which  now  rests  upon  a 
support  below  the  surface  of  the  water.  A  vessel  for  the 
collection  of  gases,  in  this  way,  is  called  a  pneumatic 
trough.  It  is  usually  a  tank  (represented  in  the  cut  as 
having  glass  sides),  in  which  jars  are  filled  with  water, 
inverted,  and  then  slid  upon  the  shelf,  the  water  being 
supported  above  its  level  by  atmospheric  pressure.  When 
the  jars  are  filled  with  gas  they  may  be  slipped  off,  mouth 
downward,  into  shallow  vessels  containing  a  little  water, 
and  kept  for  use.  In  the  foregoing  reaction  the  hydric 


172  DESCRIPTIVE   CHEMISTRY. 

sulphate  is  decomposed  by  the  zinc,  while  the  hydrogen 
is  liberated,  and  zinc  sulphate  formed.  The  changes  are 
represented  by  the  following  equation  : 

H2=S04        +   Zn.     =     Zn.=S04      +      H-H. 

Sulphuric  Acid.  Zinc.  Zinc  Sulphate.  Hydrogen  Gas. 

294  Chemical  Properties.— As  usually  prepared,  hydro- 
gen has  a  disagreeable  odor,  arising  from  the  impurities  of 
the  materials  employed;  but  pure  hydrogen  is  a  transpar- 
ent, tasteless,  inodorous  gas,  very  slightly  soluble  in  water, 
inflammable,  and  having  great  chemical  activity.  It  is  an 
essential  constituent  of  bases  and  acids,  the  latter  being 
properly  salts  of  hydrogen.  It  unites  with  metals  and 
organic  radicles,  forming  compounds  called  hydrides.  It 
does  not  support  respiration,  and  animals  immersed  in  it 
soon  die.  When  mixed  with  air  it  may  be  breathed 
without  immediate  injury,  but  from  its  tenuity  it  imparts  a 
squeaking  tone  to  the  voice.  All  attempts  to  liquefy  it, 
either  by  pressure  or  cold,  have  failed.  In  the  gaseous 
state  hydrogen  is  combined  with  itself,  forming  the  mole- 
cule, H-H. 

295.  Its  Lightness.— Hydrogen   is   the   lightest  of  all 
known  substances,  being  14-J-  times  lighter  than  air,  16  times 
lighter  than  oxygen,  and  11,000  times  lighter  than  water. 
Hence  it  may  be  carried  in   jars  with  the  open   mouth 
downward,  and   transferred    to   other  vessels   by  pouring 
upward.      Soap-bubbles  filled  with  it  rise   to  the  ceiling, 
and  it  gives  the  greatest  levity  to  balloons ;  though  they 
are  usually  inflated  with  a  hydrocarbon  gas,  the  lightness 
of  which  is  due  to  the  hydrogen  it  contains.     Owing  to 
the  fineness  of  its  molecules  it  will  escape  through  the 
joints  of  apparatus  that  are  perfectly  tight  to  other  gases ; 
and  a  stream  of  it  directed  against  one  side  of  a  piece  of 
gold-leaf  passes  through  so  rapidly  that  it  may  be  ignited 
on  the  other  side. 

296,  Inflammability  and  Explosiveness. — If  a  jet  of  hy- 


HYDROGEN. 


173 


FIG.  125. 


Exploding  Soap-Bubble* 


drogen  in  the  air  is  ignited  it  burns  with  a  pale-blue  flame, 
which  brightens  as  the  pressure  of  the  air  is  increased. 
But,  though  the  light  emitted  is  small,  the  heat  produced 
is  intense.  The  result  of  the  combustion  is  pure  water. 
If  hydrogen  and 
oxygen  gases  are 
mixed  in  the  pro- 
portion to  form 
water,  that  is, 
two  volumes  of 
H  to  one  of  O, 
and  the  mixture 
is  then  ignited  by 
an  electric  spark, 
or  the  application 
of  fire,  the  gases 

combine  explosively  with  a  sharp  report.  The  same  effect, 
though  less  intense,  is  produced  by  mingling  6ve  volumes 
of  air  with  two  of  hydrogen.  Soap-bubbles  blown  with 
such  a  mixture  detonate  when 
ignited.  (Fig.  125.)  In  ex- 
perimenting with  hydrogen,  it 
is  therefore  necessary  to  guard 
against  the  accidental  intermix- 
ture of  air  with  the  gas.  The 
lightness,  explosiveness,  and  in- 
flammability of  hydrogen,  and 
that  it  cannot  itself  sustain  com- 
bustion, may  be  all  shown  by  a 
very  simple  experiment  illus- 
trated by  Fig.  126.  If  a  jar  of 
hydrogen  be  held  mouth  down- 

,  ,  ,.    ,  ,     ,     .  i        Experiment  illustrating  the  Proper- 

Ward,  and   a   lighted   taper  be  ties  of  Hydrogen. 

introduced,  it   is   extinguished, 

while   the   gases   are  ignited  and  burn   at  the  mouth  of 

the  jar.      If,  now,  the  jar  is  inverted,  the  escaping  hy- 


FI«J.  126. 


174  DESCRIPTIVE   CHEMISTRY. 

drogen    unites   with    air,   and    there    is   a   slight   explo 
sion. 

297.  Condensation  of  Hydrogen.— But   hydrogen   and 
oxygen   may  be  ignited  without  the  application   of  fire. 
The  metal  platinum  can  he  converted  into  a  kind  of  pow- 
dery condition  known  as  platinum-sponge.     If,  now,  a  jet 
of    hydrogen   be    directed    against   a   little    ball    of   this 
sponge,  it  instantly  becomes  red-hot,  and  remains  so  as  long- 
as  the  current  lasts.     Dobereiner's  lamp  depends  upon  this 
principle.     The  theory  of  it  is  that  oxygen  is  condensed 
within  the  fine  pores  of  the  metal,  and  the  hydrogen  also 
being  condensed  by  it,  their  molecules  are  brought  within 
combining  range,  and  union  results.     But  the  porous  condi- 
tion of  the  metal  is  not  essential  to  this  action.      Clean 
strips  of  platinum  will  condense  the  gases  upon  their  sur- 
face sufficiently  to  cause  rapid  combination. 

298.  Occlusion  of  Hydrogen.— Red-hot  platinum,  palla- 
dium, and  iron,  are  freely  permeable  by  hydrogen,  and 
when  cold  are  capable  of  retaining  considerable  portions 
of  the  gas.     These  metals  are  also  capable  of  absorbing 
and  retaining  more  or  less  of  hydrogen   when  it  is  pre- 
sented to  them  in  a  nascent  state.     Graham,  who  terms 
this  effect  occlusion,  has  shown  that  palladium  takes  up 
more  than  900  times  its  volume  of  hydrogen,  and  that  the 
product  is  a  white  metallic  solid.     Graham  regarded  this 
compound  as  an  alloy,  consisting  of  palladium  and  solidi- 
fied hydrogen,  which  he  believed  to  be  a  metal,  and  called 
it  hydrogenium.     Hydrogen  in  combination  is  replaced  by 
metals,  and  undoubtedly  has  strong  analogies  with  them ; 
but  it  is  also  replaced  by  chlorine,  and  its  analogies  with 
the  chlorous  elements  are  as  numerous,  as  strongly  marked, 
and  as  important,  as  with  those  of  the  basilous  class. 

In  the  earlier  stages  of  the  science  oxygen  held  the 
leading  place ;  but,  as  we  have  seen,  hydrogen  has  usurped 
its  office  as  acid-former,  and  now  occupies  by  far  the  most 
important  chemical  position. 


CHLORINE. 


175 


CHAPTER    XII. 


THE     CHLORINE     GROUP. CHLORINE,     FLUORINE,     BROMINE, 

IODINE. 

§  1.  Chlorine  and  its  Compounds. 

CHLORINE. — Symbol,  Cl.  Atomic  Weight,  35.5 ;  Quantivalence,  I.,  III., 
V.  and  VII.  ;  Molecular  Weight,  71 ;  Molecular  Volume,  2 ;  Specific 
Gravity,  2.47. 

299.  History. — Chlorine  was  discovered  by  Scheele,  in 
1774,  but  was  long  regarded  as  a  compound.  In  1810  Davy 
established  its  elementary  character,  and  gave  it  the  name 
it  bears,  from  the  Greek  chloros,  yellowish  green.  It  is 
never  found  free  in  Nature,  but  exists  abundantly  in  the 
mineral  world,  chiefly  in  combination  with  the  metal  so- 
dium, as  common  salt. 

FIG.  127. 


Preparation  of  Chlorine. 

300.  Preparation. — Scheele's  method  of  obtaining  chlo- 
rine by  the   action   of  hydric   chloride   on    manganic   di- 


176  DESCRIPTIVE   CHEMISTRY. 

oxide  is  still  generally  adopted.  The  manganic  dioxide 
is  placed  in  a  flask  provided  with  a  safety-tube  for  pouring 
in  the  acid,  and  one  for  the  delivery  of  the  gas.  To  the 
delivery-tube  is  attached  an  intermediate  bottle  containing 
sulphuric  acid,  which  is  a  powerful  absorbent  of  water,  and 
which  dries  the  gas  by  separating  its  adhering  moisture. 
From  this  bottle  it  passes  through  a  long  glass  tube  to 
the  receiver  (Fig.  127).  A  little  acid  is  first  poured  in 
and  well  shaken  up  with  the  manganese,  in  order  to  wet 
every  portion  of  it ;  more  acid  is  then  added,  and  a  gen- 
tle heat  applied,  when  the  gas  is  given  off  copiously.  It 
may  be  collected  by  displacement,  or  over  warm  water 
in  a  pneumatic  trough.  The  chlorine,  being  heavier  than 
air,  collects  at  the  bottom  of  the  vessel,  and  the  greenish 
color  of  the  gas  will  indicate  when  the  vessel  is  filled. 
The  reaction  may  be  thus  expressed : 

MnO,  +  (HC1)4  =  MnCla  +  (H2O)3  +  Cla. 

Chlorine  may  also  be  prepared  from  common  salt  by 
the  aid  of  sulphuric  acid  and  manganic  dioxide. 

301.  Properties. — Chlorine  is  one  of  the  most  energetic 
of  bodies,  surpassing  even  oxygen  under  some  circum- 
stances. At  ordinary  temperatures  chlorine  (C1-C1)  is  a 
yellowish-green  gas,  but  by  a  pressure  equal  to  four  atmos- 
pheres, or  by  exposure  to  a  cold  of  —40°  C.,  it  may  be  con- 
densed to  a  transparent,  yellow  liquid,  of  1.38  specific 
gravity,  which  remains  unfrozen  at  —110°  C.  The  gas  has 
a  peculiar,  suffocating  odor,  and  if  inhaled,  even  when  con- 
siderably diluted,  produces  distressing  irritation  of  the 
throat  and  lungs.  When  respired,  however,  in  very  minute 
quantities,  it  is  not  only  harmless,  but  is  said  to  be  benefi- 
cial to  those  affected  with  pulmonary  disease.  Chlorine 
maintains  combustion  ;  many  bodies  burn  in  it  readily 
and  some  take  fire  in  it  spontaneously,  such  as  phosphorus, 
finely-powdered  antimony  (Fig.  128),  zinc,  and  arsenic. 
Many  organic  compounds,  rich  in  hydrogen,  are  decon> 


CHLORINE. 


177 


FIG.  128. 


C 


posed  by  it  so  rapidly  as  often  to  burst  into  flame.  A 
piece  of  paper  saturated  with  oil  of  turpentine  and  plunged 
into  a  vessel  filled  with  chlo- 
rine (Fig.  129),  emits  a  dense, 
black  smoke,  and  usually  ig- 
nites, from  the  rapid  decom- 
position of  the  turpentine. 
Hydric  chloride  is  formed  and 
carbon  deposited. 

Cold  water  absorbs  about 
two  and  a  half  times  its  own 
bulk  of  chlorine,  the  solution 
acquiring  the  color,  taste,  and 
smell  of  the  gas.  If  this  so- 
lution is  cooled  down  to  0°  C., 
a  definite  crystalline  hydrate 
of  chlorine  is  formed,  having 
the  formula  Cl5  +  H2O.  Liq- 
uid chlorine  may  be  readily 
obtained  from  these  crystals  by  hermetically  sealing  them 
in  a  curved  tube,  and  applying  a  gentle  heat.  This 
liberates  the  chlorine,  which,  pressing  upon  itself,  as- 
sumes the  condition  of  a  liquid.  It  may  be  distinguished 
from  the  water  present  by  its  yellow  color.  Chlorine  solu- 
tion readily  dissolves  gold.  Light  decomposes  chlorine- 
water,  giving  rise  to  hydric-chloride  solution  and  free  oxy- 
gen ;  hence  it  is  necessary  that  it  be  kept  in  bottles  pro- 
tected by  some  opaque  covering. 

302.  Uses.— One  of  the  most  valuable  qualities  of  chlo- 
rine is  its  bleaching  power.  Chlorine-water,  or  the  moist 
gas,  immediately  discharges  the  colors  of  ordinary  fabrics, 
indigo,  common  ink,  etc.  It  is  principally  used  in  bleach- 
ing cotton  cloth  and  rags  of  which  paper  is  to  be  made. 
Not  only  does  chlorine  destroy  the  coloring-matter  by 
uniting  with  its  hydrogen,  but  it  decomposes  the  associ- 
ated water,  setting  free  oxygen,  which,  in  its  nascent 


Combustion  of  Antimony  in  Chlorine. 


178 


DESCRIPTIVE   CHEMISTRY. 


FIG.  129. 


state,  acts  powerfully  to  oxidate  and  destroy  the  coloring 
particles.      Dry  chlorine    will   not   bleach ;    it   acts   only 
through  the  agency  of  water.     But  it  is  so 
powerful  that,  if  the  bleaching  solution  is  not 
quickly  removed,  it  corrodes  and  weakens  the 
fabric.     It  has  no  action  upon  carbon,  and 
therefore  does  not  bleach  printer's  ink.     Ar- 
gentic nitrate  (lunar  caustic)  added  to  a  solu- 
tion containing  chlorine,  or  a  soluble  chlo- 
ride, gives  a  white  precipitate  of  argentic 
chloride,  AgCl,  which  on  exposure  to  light 
changes   first    to  violet,  and  then  to  black, 
combustion  of  oil   Argentic    nitrate    is   the   test    for   chlorine. 
ChKmeentine  in   This  element  is  largely  used  in  the  prepara- 
tion of  chloride  of  lime,  in  which  form  it  is 
made  available  as  a  bleaching  agent. 

303.  Hydric  Chloride,  HC1  (Muriatic  Acid).— This  is  the 
only  compound  of  chlo- 
rine and  hydrogen  known. 
It  was  discovered  by 
Priestley  in  1772.  It  oc- 
curs in  Nature  among  the 
gaseous  products  of  vol- 
canic eruptions.  A  mixt- 
ure of  chlorine  and  hy- 
drogen gases,  when  ex- 
posed to  direct  sunlight, 
is  converted,  with  violent 
explosion,  into  hydric 
chloride.  Each  of  the 
gases  also  burns  freely 
in  an  atmosphere  of  the 
other.  If  a  jar  be  filled 
one  half  with  hydrogen, 
and  the  other  half  with  chlorine,  and  the  gases  ignited  at 
the  mouth,  an  explosion  takes  place;  and  white  fumes  of 


Direct  Union  of  Chlorine  and  Hydrogen. 


COMPOUNDS  OF  CHLORINE. 


179 


FIG.  131. 


hydric  chloride  are  formed.  A  towel  should  be  wrapped 
around  the  jar  to  prevent  the  pieces  from  scattering  in  case 
of  explosion  (Fig.  130).  Hydric  chloride  is  generally 
prepared  by  the  action  of  sulphuric  acid  on  sodic  chloride 
(common  salt).  The  reaction  is  expressed  by  the  equa- 
tion: 

2  (NaCl)  +  HaS04  =  +  Na,SO4  +  2  (HC1). 

As  the  gas  is  greedily  absorbed  by  water,  it  must  be  col- 
lected  over  mercury,  or  by  dis- 
placement.     Fig.    131    shows   a 
convenient   arrangement    for   its 
preparation. 

304.  Properties  and  Uses.— 
Hydric    chloride    is    a   colorless, 
pungent,   acid    gas,   irrespirable, 
very  irritating  to   the   eyes,  and 
extinguishes  flame.     It  is  some- 
what heavier  than  air,  having  a 
specific  gravity  of  1.24.     Under  a 
pressure   of    40    atmospheres   at 

—10°  C.,  or  of  2  atmospheres  at  —70°  C.,it  condenses  into 
a  colorless  liquid  of  1.27  specific  gravity,  which  has  never 
been  frozen.  Hydric  chloride  is  exceedingly  soluble  in 
water,  which,  at  4°  C.,  absorbs  480  times  its  volume  of  the 
gas.  This  solution  is  much  used  in  the  laboratory  as  a 
chemical  reagent. 

305.  Compounds  of  Chlorine  and  Oxygen. — The  com- 
pounds of  chlorine  and  oxygen  are  unstable,  and  most  of 
them  explosive.     Chlorine  may  act  as  a  monad,  a  triad,  a 
pentad,  or  a  heptad,  and  its  compounds  with  oxygen,  to- 
gether with  the  corresponding  acids,  are  as  follows : 

Chloric  monoxide,  C\\O  Hypochlorous  acid,  HCl'O* 
Chloric  trioxide,  Clin2O3  Hydric  chlorate,  HC1IUO3. 
Chloric  tetroxide,  C1%O4  Hydric  perchlorate,  HC1TO4. 


180  DESCRIPTIVE   CHEMISTRY. 

306.  Chloric  Monoxide,   C12O. — This    compound,   also 
known  as  hypochlorous  oxide,  may  be  obtained  by  pass- 
ing dry  chlorine  through  a  tube  filled  with  mercuric  oxide. 
A  portion  of  the  chlorine  takes  the  place  of  the  oxygen, 
forming  mercuric  chloride,  while    another  portion  unites 
with  the  oxygen,  at  the  moment  of  its  liberation,  forming 
chloric  monoxide.     As  a  gas,  its  color  is  a  shade  darker 
than  that  of  chlorine,  and  it  has  a  similar  pungent  odor. 
It  is  a  powerful  oxidizing  agent,  and  possesses  remarkably 
strong  bleaching  power. 

307.  Chloric  Tetroxide,    C12O4. — When    potassic    chlo- 
rate, KC1O6,  is  made  into  a  paste  with  sulphuric  acid  and 
cooled,  and  this  paste  is  cautiously  heated  in  a  glass  retort, 
over  a  water-bath,  a  deep-yellow  gas  is  evolved,  which  can 
only  be  collected  by  displacement.     Chloric  tetroxide  has 
a  powerful  odor,  and,  if  heated,  explodes  with  great  vio- 
lence.    It  may  be  liquefied  by  cold.     It  is  absorbed  by 
water,  the  solution  possessing  strong  bleaching  properties. 

308.  Chloric  Acid,  Hydric  Chlorate,  HC1O3.— This  com- 
pound  may  be   obtained   by  decomposing  a  solution  of 
potassic  chlorate  with  a  solution  of  hydro-fluosilicic  acid, 
the  products  being  an  insoluble  potassic  fluosilicate,  and  a 
dilute  solution  of  chloric  acid,  which,  by  cautious  evapora- 
tion at  a  low  temperature,  may  be  concentrated  to  the 
consistence  of  a  syrup.     It  is  a  very  unstable  compound, 
being   easily  decomposed,  especially  by  organic    matter, 
which  it  sometimes  ignites. 

§  2,  Fluorine  and  its  Compounds. 

FLUORINE. — Symbol,  F.    Atomic  Weight,  19 ;  Quantivalence,  I. ;  Molecu- 
lar Weight,  38  (?) ;  Molecular  Volume,  2  (?). 

309.  History. — This  substance  does  not  occur  in  Nature, 
uncombined,  and  very  little  is  known  in  regard  to  it.     Its 
most  frequent  compound  is  calcic  fluoride  (fluor-spar),  and 
from  this  it  receives  its  name.     In  consequence  of  its  great 


FLUORINE.  181 

affinity  for  other  substances,  it  has  never  been  satisfactorily 
isolated. 

310.  Hydric  Fluoride,  HF. — Hydric  fluoride  is  produced 
when  a  metallic  fluoride  (as  fluor-spar)  is  acted  upon  by 
hydric   sulphate   with   the   application   of  heat.     Hydric 
fluoride  attacks  and  corrodes  glass,  and  the  process  must, 
therefore,  be  conducted  in  vessels    of  lead   or  platinum. 
As   thus  obtained   it    is   a  colorless  gas,  which   does  not 
condense  to  a  liquid  at  —12°  C.     On  account  of  its  strong 
affinity  for  water,  it  fumes   in  the   air,  and,  if  inhaled, 
produces  intense  irritation  of  the  lungs.     The  distinguish- 
ing characteristic  of  hydric  fluoride  is  its  corrosive  action 
on   glass.      This  may  be   shown  by   placing   some   pow- 
dered calcic  fluoride,  made  into  a  paste 

*•  rir,.  164. 

with  sulphuric  acid,  in  a  leaden  cup 
(Fig.  132),  and  covering  it  with  a 
plate  of  glass,  previously  smeared  on 
one  side  with  beeswax,  through  which 
characters  have  been  traced  with  a  Action  of  Fluorine. 
fine-pointed  instrument.  The  waxed 
side  is  placed  next  the  mixture,  and  a  gentle  heat  applied 
to  the  cup.  After  the  lapse  of  half  an  hour,  on  removing 
the  glass,  and  cleaning  off  the  wax  with  the  aid  of  a  little 
oil  of  turpentine,  the  letters  will  be  found  corroded  into 
the  glass.  The  hydric  fluoride  has  reacted  upon  and  de- 
composed the  silica  of  the  glass  at  the  exposed  points. 
This  quality  is  taken  advantage  of  to  etch  the  labels  on 
glass  bottles  that  are  to  be  used  in  laboratories  and  drug- 
shops,  where  corrosive  substances  abound. 

§  3.  JBromine. 

Symbol,  Br.    Atomic  Weight,  80  ;  Quantivalence,  I.,  V.,  and  VII. ;  Molecu- 
lar Weight,  160  ;  Molecular  Volume,  2  ;  Specific  Gravity,  3.187. 

311.  History  and  Preparation. — This  substance  was  first 
obtained  by  a  French  chemist  in  1826.     The  name  bro- 


182  DESCRIPTIVE   CHEMISTRY. 

mine  is  derived  from  the  Greek  bromos,  "  stench."  It  is 
not  found  native.  After  the  extraction  of  the  crystal- 
lizable  salts  from  the  sea-water,  there  is  left  a  solution  of  the 
more  soluble  salts,  called  the  mother-liquor  or  bittern.  This 
bittern  is  rich  in  bromides,  and,  by  heating  this  with  man- 
ganic dioxide  and  hydric  sulphate,  chlorine  is  liberated 
from  the  decomposed  chlorides.  The  chlorine,  in  its  turn, 
sets  free  the  bromine  from  the  bromides,  and  the  vapors 
are  collected  in  a  cooled  receiver,  where  they  condense  into 
a  liquid. 

312.  Properties  and  Uses. — Bromine,  at  ordinary  tem- 
peratures, is  a  liquid  of  a  deep  brownish-red  color.     It  has 
a  peculiar,  irritating,  disagreeable  odor.     At  —22°  C.  it 
solidifies  to  a  hard,  brittle,  laminated  mass,  having  a  dark 
lead-gray  color  and  semi-metallic  lustre.     At  about  122° 
(50°  C.)  it  boils,  forming  red  vapors.     It  dissolves  spar- 
ingly in  water,  more  readily  in  alcohol,  and   in  all   pro- 
portions in  ether.     It  is  an  active  chemical  agent,  and  a 
violent  poison.      Bromine   is  used   in   photography,  and 
occasionally  as  a  disinfectant. 

§  4.  Iodine. 

Symbol,  I.     Atomic  Weight,  127;  Quantivalence,  I.,  III.,  V.,  and  VII.; 
Molecular  Weight,  254  ;  Molecular  Volume,  2  ;  Specific  Gravity,  4.94. 

313.  History. — Iodine  was  discovered  in  1811,  in  prod- 
ucts of  decomposition  obtained  from  the  mother-liquor, 
which   remains  when  the   ashes   of  sea-weed,  known  as 
"  kelp,"  are  leached,  and  allowed  to  crystallize.     The  name 
iodine  is  derived  from  the  Greek  ion,  "  V7iolet,"  and  refers 
to  the  color  of  its  vapor.    It  is  not  found  native.    The  prep- 
aration is  similar  to  that  of  bromine.     The  mother-liquors 
are  distilled  with  manganic  dioxide  and  hydric  sulphate, 
and  the  vapors  condensed. 

314.  Properties  and  Uses. — Iodine   is   a    grayish-black 
solid  of  metallic  lustre,  and  crystallizing  in  forms  of  the  tri- 


IODINE.  183 

metric  system.  It  melts  at  225°  (107°  C.),  and  boils  at 
356°  (180°  C.),  rising  in  dense,  beautiful,  deep-violet  vapor, 
which  is  8.72  times  heavier  than  air.  Iodine  volatilizes 
even  at  ordinary  temperatures,  diffusing  an  odor  somewhat 
similar  to  that  of  chlorine,  though  easily  distinguished 
from  it.  It  is  sparingly  soluble  in  water,  more  easily  in 
alcohol  and  ether,  or  aqueous  solutions  of  iodides.  Iodine 
colors  starch-paste  a  beautiful  deep-blue,  this  reaction  con- 
stituting the  most  delicate  test  of  its  presence.  It  stains 
the  skin  yellow,  but  is  not  so  corrosively  poisonous  as 
chlorine  or  bromine.  It  is  a  non-conductor  of  electricity. 

Iodine  is  extensively  used  in  photography,  in  the  prep- 
aration of  iodides,  as  a  chemical  reagent,  and  in  medicine. 
A  dark- brown  solution  of  iodine  in  alcohol  (containing  also 
potassic  iodide)  is  familiarly  known  as  tincture  of  iodine, 
and  much  used  as  a  liniment. 

315.  Hydric  Bromide,  HBr.,  and  Hydric  Iodide,  HI.— 
These  bodies  are  produced  by  the  action  of  dilute  sulphuric 
acid  on  bromides  and  iodides,  but  the  compounds,  espe- 
cially the  hydric   iodide,  are  liable,  under  these  circum- 
stances, to  be  further  decomposed.     By  heating  bromine 
or  iodine  with  hydrogen,  these  bodies  are  also  formed,  but 
for  practical  purposes  they  are  best  prepared  by  allowing 
bromine  and  iodine  to  react  upon  phosphorus  in  the  pres- 
ence of  water.      The  properties  of  hydric  bromide  and 
iodide  are  similar  to  those  of  hydric  chloride. 

316.  The  Halogen  Group. — The  elements  fluorine,  chlo- 
rine, bromine,  and  iodine,  constitute  a  well-marked  chemi- 
cal series,  exhibiting  a  regular  progression  of  properties. 
Chlorine  is  a  gas,  bromine  a  liquid,  and  iodine   a  solid, 
at  ordinary  temperatures.      Their  molecules  are   all   dia- 
tomic.     Chemically  they  are   highly  active   bodies,    and, 
when  brought  in  contact  with  certain  metals,  readily  give 
rise  to  a  class  of  compounds,  of  which  common  salt  is  the 
type.     Hence  they  have  been  named  halogens,  from  Greek 
words  meaning  salt-formers.      The  hydrogen  compounds 


184  DESCRIPTIVE   CHEMISTRY. 

of  these  elements,  represented  by  HF,  HC1,  HBr,  and 
HI,  also  form  a  well-marked  series.  At  ordinary  tempera- 
tures they  are  all  colorless  gases,  of  pungent,  suffocating 
odor,  and  powerful  acid  properties,  hydric  fluoride  being 
chemically  the  most,  and  hydric  iodide  the  least,  active. 


CHAPTER  XIII. 

THE    SODIUM    GKOUP — SODIUM,    POTASSIUM,    LITHIUM,   RUBID- 
IUM,   CAESIUM. 

§  1.  Sodium  and  its  Compounds. 

SODIUM. — Symbol,  Na.  (Natrium).     Atomic  Weight,  23;  Quantivalence, 
I.  and  III. ;  Specific  Gravity,  0.98. 

317.  Preparation  and  Properties.  —  Metallic    sodium, 
Na-Na,  was   first   obtained  by  Davy,  in   1807,  by  decom- 
posing  sodic   hydrate    (NaHO)    by    the    electric    current. 
Sodium  does  not  occur  native,  but  is  now  manufactured  on 
a  large  scale,  by  distilling  a  mixture  of  sodic  carbonate  and 

charcoal  at  a  high  temperature. 
Sodium,  when  freshly  cut,  presents 
a  silvery  appearance,  and,  if  cast 
upon  hot  water,  bursts  into  a  beau- 
tiful yellow  flame,  and  is  converted 
into  sodic  oxide,  or  soda  (Fig.  133). 
Sodium  is  a  very  abundant  metal, 
constituting  more  than  two-fifths 
of  common  salt,  and  existing:  as  a 

Combustion  of  Sodium. 

large  ingredient  of  rocks  and  soils. 

318.  Sodic  Chloride  (NaCl)  (Common   Salt)   may   be 
formed  by  the  direct  union  of  its  constituents,  and  is  ob- 
tained commercially,  either  by  mining  it  in  the  form  of 
rock-salt,  or  by  evaporating  the  water  of  salt-springs.     Sea- 


SODIUM   AND   ITS   COMPOUNDS.  185 

water  contains  in  every  gallon  about  four  ounces  of  salt. 
Estimating  the  ocean  at  an  average  depth  of  two  miles 
(Lyell),  the  salt  it  holds  in  solution  would,  if  separated, 
form  a  solid  stratum  140  feet  thick.  Saline  springs  in 
various  localities  in  this  country  yield  enormous  quantities 
of  salt  by  the  process  of  evaporation.  The  springs  in  the 
State  of  New  York,  alone,  furnish  an  annual  supply  of  about 
6,000,000  bushels.  As  a  solid  it  occurs  in  extensive  beds 
in  various  localities  in  Europe.  The  celebrated  bed  at 
Wielitzka,  Poland,  is  said  to  be  500  miles  long,  20  miles 
broad,  and  1,200  feet  thick,  containing  salt  enough  to  sup- 
ply the  entire  world  for  thousands  of  years. 

319.  Salt  exists  in  small  quantities  in  plants,  and  some- 
times promotes  their  growth  by  being  applied  to  the  soil. 
It  is  also  an  ingredient  of  animal  bodies,  being  contained 
in  the  blood.  It  forms  an  important  constituent  of  the 
food  of  both  man  and  beast,  an  adult  consuming  about  live 
ounces  per  week. — (PEEEIRA.) 

Common  salt  is  readily  soluble  alike  in  hot  or  cold 
water,  and  usually  crystallizes  in  cubes.  A  peculiar-shaped 

FIG.  134.  FIG.  185. 


Crystallization  of  Common  Salt. 

crystal,  or  aggregation  of  crystals,  is  often  formed  when 
the  salt  is  allowed  to  crystallize  from  concentrated  solu- 
tions. A  small  cube  is  first  formed  which  sinks  so  as  to 


186  DESCRIPTIVE   CHEMISTRY. 

bring  its  upper  surface  on  a  level,  or  a  little  below  the 
surface  of  the  water  (Fig.  134).  Other  cubes  form  on  this, 
and,  as  the  mass  sinks,  others  still  are  deposited,  each  layer 
being  attached  to  the  upper  and  outer  edge  of  the  layer 
next  below,  until  the  hopper-like  form  shown  in  Fig.  138 
is  obtained. 

320.  Uses. — Salt   is    used  lor  packing  and  preserving 
meat,  as  it  prevents  putrefaction,  by  absorbing  water  from 
the  flesh.     It  is  also  used  as  a  source  of  sodium  in  the 
manufacture  of  sodic  hydrate,  and  as  a  source  of  chlorine 
in  the  production  of  hydric  chloridQ,     It  fuses  at  a  red 
heat,  and  hence  is  used  for  glazing  stone-ware,  earthen- 
ware, etc. 

321.  Sodic  Carbonate  (Na2CO3).— Sodic  compounds  are 
supposed  to  perform  the  same  function  in  the  economy  of 
marine  plants  that  the  corresponding  potassium  compounds 
perform  in  land  plants,  and  sodic  carbonate  was  formerly 
obtained  by  leaching  the  ashes  of  the  former.     It  is  now 
manufactured    almost  entirely  from  common  salt,  by  Le- 
blanc's  process.     This  consists,  first,  in  treating  sodic  chlo- 
ride with  sulphuric  acid,  forming  crude  sodic  sulphate,  or 
salt-cake,  and  hydric  chloride.    The  next  step  in  the  process 
is  to  convert  sodic  sulphate  into  a  crude  carbonate.     This 
is  effected  by  heating  the  salt-cake  with  finely-ground  coal 
and  calcic   carbonate   (chalk)   in  a  reverberatory  furnace, 
constructed  for  the  purpose.     After  the  mass  is  thoroughly 
fused  it  is  raked  out  into  wooden  troughs,  and  allowed  to 
cool,  forming  ball-soda  or  black-ash. 

In  this  operation,  calcic  sulphide  and  carbonic  mon- 
oxide are  also  formed,  the  reaction  taking  place  according 
to  the  equation : 

Na,SO4  +  Ca"  CO3  +  40  =  Na2CO3  +  Ca"  S  +  4CO. 

The  sodic  carbonate  being  the  only  constituent  of  the 
black-ash  that  is  readily  soluble,  is  separated  by  leaching 
with  warm  water ;  and  lastly,  the  solution  is  evaporated  to 


SODIUM  AND  ITS  COMPOUNDS.  187 

dryness,  yielding  the  soda  ash  or  crude  carbonate  of  com- 
merce. When  a  hot,  filtered  solution  of  this  is  allowed  to 
cool  quietly,  large  transparent  crystals  of  a  decahydrated 
salt  (NaaCO3  +  10H2O)  are  obtained.  These  are  known 
as  sal-soda.  Sodic  carbonate  is  extensively  used  in  the 
manufacture  of  soap  and  glass,  being  both  cheaper  and 
purer  than  the  ordinary  potash.  It  is  also  used  as  a  deter- 
gent, both  in  calico-printing  and  in  the  laundry. 

322.  Hydro-Sodic  Carbonate  (NaHCO,).— This  is  pro 
duced  by  passing  carbonic  dioxide  through  a  solution  of 
sodic  carbonate.     It  is  used  under  the  name  of  saleratus, 
forms  part   of  effervescing  soda-powders,  and  is  used  in 
bread  making.- 

323.  Sodic  Hydrate,  NaKO  (Caustic  Soda).— This  com- 
pound is  obtained   by  decomposing   a  solution  of  sodic 
carbonate    (NaaCO3  +  H3O)   with   calcic   hydrate    (slacked 
lime,  CaHaOa)  at  the   boiling   temperature,  allowing  the 
calcic  carbonate  formed  to  subside,  drawing  off  the  clear 
solution  of  sodic  Irydrate,  and  concentrating  by  evaporation. 
Thus   prepared   it   is  a  white,  opaque,  brittle   substance, 
which  melts  below  red  heat,  and  volatilizes  at  higher  tem- 
peratures.    It  is  also  formed  by  the  action  of  sodium  upon 
water. 

324.  Sodic  Sulphate (NaaSO4  +  10HaO)  (Glauber's Salt). 
— This  well-known  salt  may  be  formed  by  adding  sulphuric 
acid  to  soda,  and  is  chiefly  procured  in  the  manufacture  of 
hydric  chloride.     It  has  a  bitter,  saline  taste,  and  loses  its 
water  of  crystallization  on  exposure  to  the  air. 

325.  Sodic   Nitrate,  NaNO3  (  Soda-Saltpetre).  —  Pro- 
cured native  from  parts  of   Brazil  and  Chili.     Attempts 
have  been  made  to  substitute  this  salt  for  nitrate  of  potash 
in  the  manufacture  of  gunpowder,  but  its  tendency  to  at- 
tract moisture  from  the  air  has  rendered  it  impracticable. 
Nitric  acid  is  obtained  from  sodic  nitrate,  and  it  has  been 
somewhat  used  as  a  fertilizer. 


188  DESCRIPTIVE   CHEMISTRY. 

§  2.  Potassium  and  its  Compounds. 

POTASSIUM. — Symbol,  K.  (Kalium).     Atomic  Weight,  39  ;  Quantivalence, 
I.,  III.,  and  V. ;  Specific  Gravity,  0.86. 

326.  History  and  Occurrence. — This  metal  was  discov- 
ered by  Sir  Humphry  Davy  in  1807.     He  first  obtained  it 
by  subjecting  moistened  potash  to  the  action  of  a  powerful 
voltaic  battery ;    the  positive  pole  gave   off  oxygen,  and 
metallic  globules  of  pure  potassium  appeared  at  the  nega- 
tive pole.     It  is  found  abundantly  in   Nature,  but  never 
uncombinecl.     It  is  obtained  by  the  action  of  charcoal  upon 
potassic  carbonate  at  a  very  high  temperature.     The  potas- 
sic  carbonate  is  decomposed  with  liberation  of  potassium, 
carbonic  monoxide,   and  small   quantities   of  other  com- 
pounds but  little  known.     Leaving  these  out  of  view,  the 
reaction  may  be  represented  by  the  equation : 

KaCO3  +  2C  =  300  +  K2. 

327.  Metallic  Potassium  (Molecule)  (K-K),  at  common 
temperatures,  is  a  silver-white  metal,  and  so  soft  that  it 

may  be  moulded  like  wax.    If  thrown 
•> 

upon  the  surface  of  water,  instant 
decomposition  takes  place  (Fig.  139), 
potassic  oxide  being  at  first  formed. 
The  liberated  hydrogen,  together 
with  a  small  quantity  of  volatilized 
metal,  is  ignited  by  the  heat  evolved 
during  the  decomposition,  and  burns 
with  a  beautiful  lilac  flame  as  the 
Combustion  of  Potassium,  g^ule  floats  about  on  the  surface  of 
the  liquid.  At  the  close  of  this  reac- 
tion a  second  change  ensues :  the  potassic  oxide,  which  had 
been  kept  above  the  surface  of  the  water,  coming  in  contact 
with  the  liquid,  gives  rise  to  the  formation  of  potassic  hy- 
drate, which  becomes  red-hot,  and  scatters  with  a  violent 
explosion.  Potassium  decomposes  nearly  all  compounds 


POTASSIUM  AND   ITS   COMPOUNDS.  189 

containing  oxygen,  if  brought  in  contact  with  them  at  high 
temperatures,  and  many  even  at  ordinary  temperatures. 
Hence,  to  preserve  it  pure,  it  is  kept  in  naphtha,  a  liquid 
containing  no  oxygen. 

328.  Potassic  Monoxide  (K2O). — This  compound  is  ob- 
tained by  exposing  metallic  potassium  to  perfectly  dry  air, 
free  from  carbonic  dioxide,  at  ordinary  temperatures.     It 
is  a  white  solid,  which  melts  at  a  red  heat,  and  volatilizes  at 
higher  temperatures.     It  is  very  deliquescent ;  brought  in 
contact  with  water  it  becomes  incandescent,  potassic  hy- 
drate being  produced. 

329.  Potassic  Hydrate  (KHO)  ( Caustic  Potash).— The 
method  of  obtaining  this  important  substance  is  similar  to 
that  of  obtaining  caustic  soda.     The  solution  of  potassic 
hydrate,  after  being  boiled  until  the   temperature  of  the 
liquid  is  near  a  red  heat,  flows  without  ebullition,  and  may 
be  run  into  moulds,  solidifying  on    cooling   to   a    white, 
hard,  brittle  substance,  which  melts,  below  redness,  to  an 
oily  liquid,  and  volatilizes  at  a  full  red  heat  in  white,  pungent 
vapors.     Potassic  hydrate  dissolves  freely  in  water,  with 
great  evolution  of  heat.   It  has  a  peculiar  nauseous  odor,  and 
acrid  taste.     It  decomposes  acids  with  formation  of  corre- 
sponding potassic  salts  and  elimination  of  water,  changes 
vegetable  yellows  to  brown,  restores  the  blues  discharged 
by  acids,  and  decomposes  animal  and  vegetable  substances, 
whether  living  or  dead.     It  is  used  in  medicine  to  cauterize 
and  cleanse  ulcers  and  foul  sores ;  hence  its  name,  caustic 
potash.     If  a  solution  of  potash  be  shaken  in  a  bottle  with 
any  fixed  oil,  the  two  unite,  forming  a  soap.     This  accounts 
for  the  soft,  greasy  feel  it  has  when  touched  by  the  fingers, 
as  it  decomposes  the  skin  and  forms  a  soap  with  its  oily 
elements.     When  taken  into  the  system,  potash  acts  as  a 
powerfully  corrosive  poison.     Its  active  chemical  character 
renders  it  an  indispensable  reagent  in  the  laboratory. 

330.  Potassic  Chloride  (KC1)  is  known  as  the  mineral 
sylvite,  and  is  isomorphous  with   NaCl.      Potassic  iodide 


190  DESCRIPTIVE   CHEMISTRY. 

(KI)  may  be  formed  by  adding  iodine  to  a  solution  of  pot- 
ash, and  gently  warming  until  the  solution  assumes  a 
brown  tint.  It  is  a  very  soluble,  white  solid,  which  crys- 
tallizes in  cubes,  and  is  much  used  in  medicine. 

331.  Potassic   Carbonate    (K2CO3).— Potassic   salts   of 
various  kinds  exist  in  the  juices  of  plants.     By  the  com- 
bustion of  the  plants,  most  of  these  are  decomposed  with 
the  formation  of  potassic  carbonate,  which  may  be  obtained 
from  their  ashes.     This  is  a  highly  alkaline,  deliquescent 
salt,  and  is  used  largely  in  the  manufacture  of  soap  and 
glass,  in  preparing  caustic  potash,  etc.     It  is  also  an  im- 
portant reagent  in  the  laboratory,  and  a  most  valuable 
fertilizer.      This  salt  rarely  forms  less  than  20  per  cent., 
and  sometimes  more  than  50  per  cent.,  of  the  weight  of 
wood-ashes.     The  ashes  of  different  plants,  and  even  dif- 
ferent parts  of  the  same  plant,  yield  it  in  varying  quantities. 
Wood  ashes  furnish  the  principal  source  of  the  potassic 
carbonate  of  commerce,  from  which  it  is  obtained  by  leach- 
ing them  and  boiling  the  solution  to  dryness  in  iron  pots. 
The  residue  is  called  potashes,  and  these,  when  calcined, 
afford  the  impure  carbonate  known  as  pearlash.     Potash, 
or  pearlash,  therefore  represents  the  readily  soluble  portion 
of  wood-ashes,  and  consists  chiefly  of  potassic  carbonate 
with  small  amounts  of  sodic  carbonate  and  common  salt. 

332.  Hydro-Potassic  Carbonate    (KHC03).— This    is 
formed  by  passing  carbonic  dioxide  through  a  strong  solu- 
tion of  potassic  carbonate.     It  is  employed  as  a  source  of 
potassium  in  the  formation  of  many  of  its  other  compounds, 
and  is  also  used  for  making  effervescing  draughts,  by  add- 
ing citric  or  tartaric  acid  to  its  solution. 

333.  Potassic  Nitrate  (KNO3)  (Nitre,  Saltpetre). — This 
salt  occurs  as  a  native  product  in  the  earth  of  various  dis- 
tricts in  the  East  Indies,  and  is  separated  therefrom  by 
leaching  the  soil,  and  allowing  the  nitre  to  crystallize.     It 
is  artificially  formed   by  heaping  up  organic  matter  with 
lime,  ashes,  and  soil,  and  keeping  the  mass  well  moistened 


POTASSIUM  AND   ITS   COMPOUNDS.  191 

with  urine  for  a  period  of  two  or  three  years,  when  the 
heap  is  lixiviated  and  the  salt  crystallized  out.  Besides 
these  sources,  nitre  occurs  in  the  sap  of  certain  plants,  such 
as  the  sunflower,  tobacco-plant,  etc.  Nitre  dissolves  in 
about  three  times  its  weight  of  cold  and  one-third  its 
weight  of  boiling  water.  When  thrown  upon  burning 
charcoal  it  is  decomposed  and  deflagrates  violently.  Paper 
dipped  in  a  solution  of  sodic  nitrate,  and  dried,  forms  what 
is  known  as  touch-paper.  When  ignited,  it  burns  slowly 
and  steadily  until  consumed ;  hence  its  use  in  lighting 
trains  of  gunpowder,  fireworks,  etc.  Nitre  has  a  cooling, 
saline  taste  and  strong  antiseptic  powers.  Owing  to  the 
latter  quality  it  is  used  extensively  in  packing  meat,  to 
which  it  imparts  a  ruddy  color.  It  is  chiefly  consumed, 
however,  in  the  manufacture  of  gunpowder. 

334.  Gunpowder  is  an  intimate  mechanical  mixture  of 
about  1  part  nitre,  1  part  sulphur,  and  3  parts  charcoal. 
These  proportions,  however,  vary  somewhat  in  different 
countries,  as  well  as  in  different  sorts  of  powder.  More 
charcoal  adds  to  its  power,  but  also  causes  it  to  attract 
moisture  from  the  air,  which  of  course  injures  its  quality. 
For  blasting  rocks,  where  a  sustained  force,  rather  than  an 
instantaneous  one,  is  required,  the  powder  contains  more 
sulphur,  and  is  even  then  often  mixed  with  sawdust  to 
retard  the  explosion.  The  nitre,  sulphur,  and  charcoal, 
having  been  ground  and  sifted  separately,  are  thoroughly 
mixed  and  then  made  into  a  thick  paste  with  water.  This 
is  ground  for  some  hours  under  edge  stones,  after  which  it 
is  subjected  to  immense  pressure  between  gun-metal  plates, 
forming  what  is  known  as  press-cake.  These  cakes  are 
then  submitted  to  the  action  of  toothed  rollers,  whereby 
the  granulation  of  the  powder  is  effected.  The  grains 
thus  formed  are  sorted  by  means  of  a  series  of  sieves, 
and  thoroughly  dried  at  a  steam  heat.  The  last  opera- 
tion, that  of  polishing,  is  accomplished  in  revolving  bar- 
rels, after  which  the  powder  is  readv  for  market.  The 
9 


192  DESCRIPTIVE   CHEMISTRY. 

heavier  the  powder,  the  greater  is  its  explosive  power. 
Good  powder  should  resist  pressure  between  the  fingers, 
giving  no  dust  when  rubbed,  and  have  a  slightly  glossy 
aspect.  The  explosive  power  of  gunpowder  is  due  to  a 
sudden  formation  of  a  large  volume  of  nitrogen  and  car- 
bonic dioxide;  one  volume  of  the  powder  giving  about 
1,800  volumes  of  vapor.  Fireworks  contain  nitre  as  a 
chief  ingredient,  mixed  with  charcoal,  sulphur,  ground 
gunpowder,  and  various  coloring  substances. 

335.  Potassic  Sulphate  (K2SO4)  is  obtained  in  the  man- 
ufacture  of  hydric   nitrate,  and  is  of  limited  use  in  the 
arts.     Potassic  chlorate  (KC1O3)   may  be  formed  by  pass- 
ing chlorine  gas  through  a  solution  of  potassic  carbonate 
(K2CO3).     Potassic  chlorate  is  soluble  in  water,  has  a  taste 
resembling  that  of  nitre,  melts  at  about  700°,  and,  if  heated 
above  that  temperature,  decomposes  with  formation  of  po- 
tassic chloride  and  perchlorate,  and  oxygen  gas.     It  is  used 
in  the  manufacture  of  lucifer  matches,  in  certain  operations 
of  calico-printing,  and  as  a  source  of  oxygen. 

336.  Sodic  and  Potassic  Silicates.— If  8  or  10  parts  of 
sodic  or  potassic  carbonate  are  mixed  with  12  or  15  parts  of 
sand  and  1  of  charcoal,  on  being  heated  they  melt,  and  form 
a  mass  resembling  ordinary  glass ;  but  it  entirely  dissolves 
in  hot  water.     This  is  known  as  soluble  glass,  and  when 
applied  to  wood  and  other  substances  answers  the  protec- 
tive purpose  of  a  varnish  or  paint. 

337.  Soap. — When  caustic  potash,  or  soda,  acts  upon 
certain  organic  acid  radicles,  chiefly  oleine  and  stearine, 
which  are  present  in  fats  and  oils,  the  resulting  salts  are 
termed  soaps,  and  the  process  by  which  they  are  produced 
is  called  saponification.     The  consistence  of  soap  depends 
chiefly  upon  its  alkali.     Hard  soaps  are  made  of  soda,  or  a 
mixture  of  soda  and   potash,  while  in   soft  soaps  potash 
alone  is  used,  the  soaps  made  with  this  base  being  deliques- 
cent and  consequently  attracting  water,  which  renders  the 
soap  liquid.     The  quality  of  hardness  is  due  to  the  con- 


LITHIUM,   RUBIDIUM,   (LESIUM.  193 

sistence  of  the  oil  or  fat.  The  compounds  containing  a  large 
proportion  of  stearin  and  palmitin,  like  tallow,  form  hard 
soaps,  while  those  in  which  olein  predominates,  as  the  soft 
fats  and  oils,  produce  soap  of  softer  consistence.  The 
glycerin  which  is  retained  in  soft  soap  also  adds  to  its 
fluidity.  Soap  has  a  powerful  affinity  for  water,  and  may 
retain  from  50  to  60  per  cent,  of  it  and  still  continue  solid ; 
hence  dealers  frequently  keep  it  in  damp  places  where  it 
will  absorb  moisture.  It  is  soluble  in  fresh  water,  but, 
with  the  exception  of  cocoa-soap,  is  insoluble  in  salt-water. 

338.  Mode  in  which  Soap  acts  in  Cleansing. — As  water, 
having  no  affinity   for  oily   substances,   will  not  dissolve 
them,  of  course  it  cannot  alone  remove  them  from  surfaces 
to  which  they  may  adhere.     The  oily  matters  which  are 
constantly  exuding  from  the  glands  of  the  skin,  uniting 
with  the  outer  dust,  form  a  film  over  the  body.     The  alkali 
of  the  soap  acts  upon  the  oil  during  ablution,  partially 
saponifies  it,  and  renders  the  unctuous  compound  freely 
miscible  with  water,  so  as  to  be  easily  removed.     The  cuti- 
cle or  outer  layer  of  the  skin  is  chiefly  composed  of  albu- 
men, which  is  soluble  in  the  alkalies.     The  alkali  of  the 
soap,  therefore,  dissolves  off  a  portion  of  the  cuticle  with 
the  dirt ;  every  washing  with  soap  thus  removing  the  old 
face  of  the  scarf-skin  and  leaving  a  new  one  in  its  place. 
The  action  of  soap  in  cleansing  textile  fabrics  is  of  a  similar 
nature.     Alkalies  not  only  act  upon  greasy  matter,  but,  as 
is  well  known,  dissolve  all  organic  substances.     In  the  case 
of  soap,  however,  the  solvent  power  of  the  alkali  is  in  part 
neutralized,  thus  preserving  both  the  texture  and  color  of 
the  fabric  exposed  to  its  action.     The  oily  nature  of  the 
soap  also  increases  the  pliancy  of  the  articles  washed. 

§  3.  Lithium,  Rubidium,  Caesium. 

339.  History. — These   three  rare   elements  are  found 
associated  with  potassium  and  sodium,  to  which  they  are 
closelv  allied  in  all  their  chemical  Delations.     Lithium  is  a 


194  DESCRIPTIVE  CHEMISTRY. 

brilliant,  silver- white  metal,  softer  than  lead,  remarkably 
light,  having  a  specific  gravity  of  0.578.  We  have  already 
referred  to  its  distribution  (201). 

Rubidium,  also  a  soft,  white  metal,  was  discovered  by 
means  of  the  spectroscope.  Its  spectrum  contains  two 
dark-red  lines;  hence  its  name,  from  the  Latin  rubidus, 
meaning  dark-red.  Rubidium  has  been  found  in  the  ashes 
of  many  plants,  in  mineral  water,  in  tobacco-leaves,  in 
coffee,  tea,  cocoa,  and  crude  tartar. 

Caesium  was  discovered  at  the  same  time  with  rubidium. 
The  name  comes  from  ccesius,  sky-blue,  and  has  reference 
to  two  blue  lines  in  the  spectrum. 


CHAPTER  XIV. 

SILVER. — GOLD. — BORON. 

§  1.  Silver  and  its  Compounds. 

SILVER. — Symbol,  Ag.  (Argentum).    Atomic  Weight,  108;  Quautivalence, 
I.  and  III. ;  Specific  Gravity,  10.5. 

340.  Metallic  Silver  (Molecule)  (Ag-Ag).— This  well- 
known  metal  is  frequently  found  native  in  fibrous  crystal- 
line masses.  It  is  also  found  in  combination  with  chlorine, 
sulphur,  arsenic,  or  antimony.  The  principal  silver-mines 
are  those  of  Mexico  and  Peru.  Silver  is  obtained  from  its 
ores  by  various  processes,  in  some  of  which  the  ore  is 
roasted  with  common  salt,  by  which  argentic  chloride  is 
formed ;  then,  together  with  water,  iron-scraps,  and  mer- 
cury, put  into  casks  which  revolve  on  their  axes.  The  iron 
removes  the  chlorine,  and  the  mercury  amalgamates  with 
the  silver,  from  which  it  is  afterward  freed  by  distillation 

(in.). 

From  plumbic  sulphide,  which  is  by  far  the  most  im- 
portant source  of  silver,  it  is  obtained  by  first  smelting  for 
lead,  and  then  volatilizing  the  lead  by  cupellation,  a  pe- 


SILVER  AND   ITS  COMPOUNDS.  195 

culiar  process,  conducted  in  a  furnace,  the  shallow,  basin- 
shaped  bottom  of  which  is  covered  with  a  thick  layer  of 
bone,  ashes,  marl,  or  some  other  porous,  infusible  material. 
When  the  lead,  alloyed  with  a  small  quantity  of  silver,  is 
melted  on  this  hearth,  in  a  current  of  air,  most  of  the  lead 
oxidizes ;  the  oxide  or  litharge  melts,  and,  being  absorbed 
by  the  cupel,  leaves  the  silver  pure. 

341.  Properties  and  Uses. — Silver  is  the  whitest  of  the 
metals,  with  a  bright,  metallic   lustre.     It  is  very  malle- 
able, ductile,  and  tenacious.      It  may  be  extended  into 
leaves  not  exceeding  1 6  0*0  0  0  of  an  inch,  or  ^^5^5-  of  a  milli- 
metre, in  thickness;   and  one  grain,  or  ^  of  a  gramme, 
may  be  drawn  out  into  400  feet,  or  122  metres  of  wire. 
Silver  does  not  oxidize  in  the  air  at  any  temperature,  hut 
absorbs  oxygen  when  melted,  holding  it  mechanically,  and 
giving  it  off  on  solidifying.     It  is  a  good  conductor  of  heat 
and  electricity,  and  its  polished  surface  is  one  of  the  best 
reflectors  of  light.     Silver  is  chiefly  consumed  in  the  manu- 
facture of  allo}-s  used  for  coinage  and  silver-plate.     Being 
too  soft,  pure  silver  is  never  employed  for  these  purposes. 

342.  Argentic  Chloride  (AgCl.)  (Chloride  of  Silver)  is 
occasionally  found  native   in  mines,  and  is   called  horn 
silver,  from  its  tough,  horny  texture.     It  may  be  prepared 
artificially  by  adding  a  solution  of  common  salt  to  a  solu- 
tion of  argentic  nitrate,  and  appears  as  a  white  powder 
which  darkens  in  color  on  exposure  to  light.     Argentic 
bromide   (AgBr-)  and  argentic  iodide  (Agl)  resemble  the 
previous  compound,  and  are  found  in  a  similar  way. 

343.  Argentic  Monoxide  (Ag2O)  (Silver  Oxide).— This 
substance  is  best  prepared  by  mixing   concentrated  hot 
solutions  of  argentic  nitrate  and  potassic  hydrate.     It  is  a 
black  or  bluish-black,  heavy  powder,  slightly  soluble  in 
water.      It  is  also   formed  when    silver  is   heated    in  the 
air,  but  at  a  red  heat,  or  even  lower  temperatures,  it  is 
completely  decomposed,  with  formation  of  metallic  silver 
and  oxygen  gas. 


196  DESCRIPTIVE   CHEMISTRY. 

344.  Argentic  Nitrate   (AgNO3)    (Lunar    Caustic). — 
This  interesting  salt  may  be  obtained  by  dissolving  metal- 
lic silver  in  nitric  acid  ;  colorless,  anhydrous  crystals  being 
formed,  which  are  readily  soluble  in  an  equal  weight  of 
cold  water.     These   crystals,  when  melted  and    cast  into 
small  sticks,  form  the  lunar  caustic  of  surgery.     Argentic 
nitrate    solution  is  decomposed    by  organic    matter,  with 
separation  of  black,  finely-divided  metallic  silver,  the  reac- 
tion being  most  rapid   when  taking  place  in  the    light. 
Advantage  is  taken  of  this  property  in  making  indelible 
ink  and  hair-dye.     A  solution  of  potassic  cyanide  removes 
the  stain  thus  produced. 

§2.    Gold. 

Symbol,  Au.  (Auruin).     Atomic  Weight,   196.6 ;  Quantivalence,  I.  and 
III. ;  Specific  Gravity,  19.34. 

345.  Gold  (molecular  symbol  of  metal  probably  [Au=Au]). 
— This  is  one  of  the  most  widely  diffused  of  the  metals,  and 
generally  occurs  in  minute   grains,  though   sometimes  in 
masses  weighing  many  pounds.     In  1851  a  lump  weighing 
106  pounds  was  found  in  Australia,  embedded  in  a  matrix 

of  quartz.     It  sometimes  occurs  in  crys- 
talline form,  as  shown  in  Fig.  140.     As 
found  in  Nature,  gold  is  rarely  pure,  but 
generally  mixed  with  a  variable  quantity 
of  silver.     Gold  is  separated  from  all  the 
constituents  of  its  ores  except  silver,  by 
amalgamation  with    mercury.     It  is    ob- 
tained from  silver  by  boiling  the  alloy  in 
nitric  acid,  which  dissolves  out  the  silver, 
Crystal  of  Gold.        leaving  the  gold  pure.     In  this  operation, 
in  order  to  prevent  the  silver  from  being 
mechanically  protected  from  the  action  of  the  acid,  it  is 
necessary  that  there  should  be  three  times  as  much  silver 


BORON  AND  ITS  COMPOUNDS.          197 

as  gold.     As  the  gold  constitutes  only  one  quarter  of  the 
mass,  the  process  is  known  as  quartation. 

346.  Properties. — Gold  is  the  only  metal  of  a  yellow 
color,  it  has  a  brilliant  lustre,  and  high  specific  gravity. 
It  is  the  most  malleable  of  the  metals,  and  to  its  ductility 
there  is  scarcely  a  limit ;  when  pure  it  is  nearly  as  soft  as 
lead.     It  fuses  at  about  1200  C.,  and  does  not  oxidize  in 
the  air  at  any  temperature.     Gold  is  not  dissolved  by  any 
single  acid,  but  is  acted  upon  by  chlorine,  or  any  solution 
which  liberates  the  gas.     Its  usual  solvent  is  a  mixture  of 
four  parts  of  hydric  chloride  and   one  of  hydric  nitrate, 
called,  on  account  of  its  power  to  dissolve  gold,  aqua  regia. 
The  compounds  of  gold  have  little  chemical  interest  to  the 
ordinary  student.     AuCl,  is  somewhat  used  in  the  labora- 
tory, and  a  solution  of  auric  cyanide  in  potassic  cyanide  is 
used  in  electro-gilding. 

§  3.  Boron  and  its  Compounds. 

BORON. — Symbol,  B.   Atomic  Weight,  II. ;  Quantivalence,  III. ;  Molecular 
Weight,  22  (?) ;  Molecular  Volume,  2 ;  Specific  Gravity,  2.68. 

347.  Boron. — This  substance   is  not  found  native,  but 
may  be  prepared  by  decomposing  fused  boric  oxide  (B2O3) 
with  sodium  or  aluminium.     It  exists  in  several  modifica- 
tions, being  either  brown,  amorphous,  and  slightly  soluble 
in  water,  or  crystalline,  and  entirely  insoluble.     One  of  the 
two   crystalline  modifications  known  is  exceedingly  hard 
and  brilliant,  resembling  the  diamond  in  this  respect. 

348.  Boric  Acid,    H3BO3.— This    acid    is    found   as   a 
natural  constituent  of  hot  mineral  springs,  the  principal 
locality  being  the  "  lagoons "  of  the  volcanic  district  of 
Tuscany,  where  the  acid  issues  from  the  earth  with  jets 
of  steam,   and   is   collected    by    throwing   the   jets   into 
water.     The  acid  is  afterward  separated  from  the  water 
by  evaporation  in  leaden  pans  so  arranged  that  they  are 
heated  by  the  vapors  as  they  escape  from  the  earth.     It  is 


198  DESCRIPTIVE   CHEMISTRY. 

deposited  in  white,  scaly  crystals,  which  are  purified  by 
repeated  crystallizations.  These  crystals  have  a  glassy- 
appearance,  and  are  soapy  to  the  touch.  They  dissolve 
much  more  readily  in  boiling"  than  in  cold  water,  and  form 
a  solution  having  feebly  acid  properties. 

349,  Hydro-Sodic  Borate  (Na2H2B4O8  +  9H2O)  (Borax). 
— This  salt  is  found  native  at  the  bottom  of  certain  lakes 
in  Thibet  and  California.  It  is  procured  artificially  by 
heating  boric  acid  with  sodic  carbonate,  decomposition 
taking  place  with  evolution  of  carbonic  dioxide.  Borax 
has  an  alkaline  taste  and  reaction,  and  in  the  fused  state, 
at  a  high  heat,  possesses  the  property  of  dissolving  many 
metallic  oxides ;  hence  its  use  as  a  flux  in  the  welding  of 
metals.  It  dissolves  the  coating  of  oxide  formed  when 
the  metals  are  heated,  which  thus  constantly  present  a  clean 
surface.  On  account  of  the  same  property  it  is  one  of  the 
most  important  reagents,  being  chiefly  employed  in  blow- 
pipe analysis. 


CHAPTER   XV. 

THE   NITROGEN   GKOUP. — NITROGEN,   PHOSPHORUS,  ARSENIC, 
ANTIMONY,    BISMUTH. 

§  1.  Nitrogen  and  its  Compounds. 

NITROGEN. — Symbol,  N.  Atomic  Weight,  14 ;  Quantivalence,  L,  III.,  and 
V. ;  Molecular  Weight,  28  ;  Molecular  Volume,  2  ;  Specific  Gravity, 
0.972. 

350.  Nitrogen  Gas  (Molecule)  (NiN).— This  gas  was 
discovered  by  Rutherford,  in  1772.  Chaptal  afterward 
gave  it  the  name  nitrogen,  signifying  generator  of  nitre. 
It  is  very  extensively  diffused  in  Nature,  forming  about 
four-fifths  of  the  atmosphere,  in  which  it  plays  the  impor- 
tant part  of  diluting  the  oxygen,  and  adapting  it  to  the 
conditions  of  life.  It  is  the  characteristic  ingredient  of 


NITROGEN   AND   ITS  COMPOUNDS. 


FIG.  141. 


Preparation  «»f  Nitrogen. 


animal  tissue,  and  is  never  entirely  absent  from  plants, 
while  of  many  important  vegetable  products  it  is  an  essen- 
tial constituent,  as  for  example,  of  the  vegetable  alkaloids. 

351.  Preparation. — Nitrogen   is   most  commonly  pre- 
pared by  withdrawing  the  oxygen  from  a  portion  of  air. 
A  small  bit  of  phosphorus  is 

placed  in  a  little  cup  and 
floated  on  the  water  in  a  pneu- 
matic trough.  It  is  then  set 
on  fire  and  a  jar  placed  over 
it,  as  in  Fig.  141.  The  phos- 
phorus takes  the  oxygen, 
forming  phosphoric  pentox- 
ide,  which  fills  the  jar  with  a 
white  vapor ;  but  this  is  soon 
absorbed  by  the  water,  and 
nitrogen  alone  is  left,  the 
water  rising  to  occupy  the 
space  of  the  vanished  oxygen. 

352.  Properties. — Nitrogen  is  a  transparent  gas,  without 
taste  or  color,  and  has  never  been  condensed  into  a  liquid. 
It  is  remarkable  for  chemical  inertness.     It  is  irrespirable ; 
animals  placed  in   it  quickly  die,  not  from  its  poisonous 
action,  but  from  lack  of  oxygen.     It  supports   the  com- 
bustion of  but  few  substances;  a  lighted  taper  introduced 
into  it  is  immediately  extinguished.     Boron,  titanium,  and 
a  few  other  rare  bodies,  burn  in  it,  with  the  formation  of 
nitrides.      It   is   slightly  soluble   in  water,  one  hundred 
volumes  of  the  latter,  at  15°  C.,  taking  up  about  one  and 
a  half  volume  of  the  gas.     Although  nitrogen  combines 
directly  with  only  two  elementary  substances,  boron  and 
titanium,  it  has  great   capacity  for   combination,  and    is 
distinguished  by  the  large  number  and  variety  of  its  com- 
pounds. 

353.  Hydric  Nitride  or  Ammonia   (H3N). — This  sub- 
stance was    first   described   by  Priestley,  in  1774.     It  is 


200  DESCRIPTIVE   CHEMISTRY. 

frequently  met  with  in  Nature,  being  a  constant  product 
of  the  decomposition  of  organic  substances  which  contain 
nitrogen.  It  is  produced  from  the  destructive  distillation 
of  horns  and  hoofs,  which  are  rich  in  nitrogen,  but  the 
chief  source  of  commercial  ammonia  is  the  liquor  of  the 
gas-works.  Ammonia  gas  is  conveniently  obtained  by  the 
action  of  one  part  of  quick-lime,  CaO,  upon  two  parts  of 
ammonic  chloride,  NH3HC1,  in  a  glass  flask  or  retort.  The 
reaction  is  thus  shown  : 

(NH3HC1)2  +  CaO  =  CaCl2  +  H3O  +  (H3N)2. 

It  will  be  seen  that  the  lime  takes  the  hydric 
chloride,  forming  calcic  chloride,  while  water  and 
ammonia  are  set  free.  The  gas  may  be  collected 
in  jars  in  the  pneumatic  trough,  but  it  must  be 
over  mercury,  as  water  absorbs  it.  It  is,  how- 
ever, more  convenient  to  procure  it  by  what  is 
called  the  method  of  displacement.  The  gas 
generated  in  the  lower  vessel  (Fig.  142)  being 
lighter  than  the  air,  accumulates  in  the  upper 
portion  of  the  inverted  jar,  displacing  the  air 
and  expelling  it  downward. 

354.  Properties. — Ammonia  is  a  colorless,  ir- 
respirable  gas  of  a  pungent,  caustic  taste,  lighter  than  air 
(sp.  gr.  0.59),  and  possesses  strong  alkaline  properties, 
changing  vegetable  blues  to  green  and  yellows  to  brown, 
whence  it  is  called  volatile  alkali.  It  does  not  support  com- 
bustion or  respiration ;  a  thin  stream  of  the  gas  may  be  ig- 
nited in  the  air,  and  burns  with  a  pale  flame.  It  may  be  con- 
densed by  cold  or  pressure,  both  to  the  liquid 
and  the  solid  state.  Liquid  ammonia  is  a 
colorless,  mobile  fluid.  In  the  solid  state  it 
is  white,  transparent,  and  crystalline.  From 
the  circumstance  that  it  was  derived  from  the 
horns  of  harts,  it  was  called  spirits  of  harts- 
horn. Ammonia  is  recognized  by  its  odor.  Testing  Ammonia. 


• 


NITROGEN   AND   ITS   COMPOUNDS. 


201 


If  a  rod  dipped  in  hydric  chloride  be  brought  near  a  source 
of  ammonia,  a  white  cloud  is  produced  by  the  formation  of 
ammonic  chloride  (NH4C1).  (Fig.  143). 

355,  Uses. — Ammonia  is   used    medicinally  in  various 
ways.     It  is  administered  internally  as  a  stimulant,  and 
applied    externally   as    a    counter-irritant.      Mixed   with 
olive-oil,  it  forms  volatile  liniment.     It  is  the  best  antidote 
to  prussic  acid,  but  in  large  doses  it  is  poisonous.     It  is  of 
many  uses  to  the  chemist. 

356.  Oxides  and  Acids  of  Nitrogen. — Nitrogen  combines 
with  oxygen,  forming : 


Nitric  monoxide,  N'2O. 
Nitric  dioxide,  Nin,Oa. 
Nitric  trioxide,  Nin2O3. 
Nitric  tetroxide,  NvaO4. 
Nitric  pentoxide,  NV3O5. 


Nitrous  acid,  HN'"O,. 
Nitric  acid,  HNVO8. 


FIG.  144. 


357.  Nitric  Monoxide  (NaO)  (Nitrous  Oxide).—  This 
compound  was  discovered,  in  1776,  by  Priestley,  and 
further  examined  by  Davy  in  1800,  who  noticed  the  ex- 
hilarating effects  produced 
by  the  respiration  of  this 
gas,  from  which  its  popular 
name,  "laughing  gas"  is 
derived.  It  is  prepared 
from  ammonic  nitrate,  by 
moderately  heating  this  salt 
in  a  flask.  The  gas  escapes 
through  a  tube,  and  is  col- 
lected in  jars  Over  Water 
(Fig.  144).  It  should  be 

allowed  to  stand  for  some  time  over  water,  to  absorb  any 
nitrous  acid  that  may  chance  to  be  formed.  The  chemical 
change  may  be  represented  by  the  equation, 

N,H408  =  2H90  +  N30, 


Preparation  of  Nitrous  Oxide. 


202  DESCRIPTIVE   CHEMISTRY. 

one  molecule  of  ammonic  nitrate  yielding  two  molecules 
of  water  and  one  of  nitric  monoxide. 

358.  Properties. — At  ordinary  temperatures  nitric  mon- 
oxide is  a  neutral,  colorless,  transparent  gas,  of  a  slightly 
sweetish   taste,   and   very  soluble   in  water — cold   water 
absorbing  about  three-fourths  of  its  volume.     Sp.  gr.  1.527. 
It  is  an  active  supporter  of  combustion,  relighting  a  glow- 
ing  candle  when  plunged  into   it,  and  intensifying  the 
combustion  of  phosphorus  almost  equally  with  pure  oxy- 
gen.    A  pressure  of  50  atmospheres  at  45°  F.  condenses  it 
into  a  clear  liquid  which  boils  at  about  1126°  F.,  and  may 
be  frozen  at  about  — 150°  F.      When    breathed  in   small 
quantities  this  gas  produces  a  transient  intoxication,  at- 
tended sometimes  by    an  irresistible  propensity  to  laugh, 
and  at  others    by  a  tendency  to  muscular  exertion,  indi- 
viduals being  variously  affected  according  to  temperament. 
The  gas  should   be  pure,  and  even  then  the  experiment 
is  not  a  safe  one  for  some  constitutions.     Inhaled  in  larger 
quantities  it  produces  insensibility,  hence  it  is  now  much 
employed  by  dentists  as  an  anaesthetic. 

359.  Hydric  Nitrate  or  Nitric  Acid    (HNO3).— This 
compound,  familiarly  known  as  aqua-fortis,  is  not  found  in 
Nature,  but  has  been  known  since  very  early  times.     It  is 

FIG.  14.-. 


Liberation  of  Nitric  Acid. 


produced  on  a  large  scale  by  the  decomposition  of  sodic 
nitrate  with  sulphuric  acid :  100  parts,  by  weight,  of  sodic 


NITROGEN  AND   ITS  COMPOUNDS.  203 

nitrate,  117  parts  concentrated  sulphuric  acid,  and  30  parts 
of  water,  are  placed  in  a  glass  retort  which  is  supplied  with 
a  receiver  .Z?,  kept  cool  by  cold  water  flowing  over  it  from 
the  tube  /,  by  means  of  a  netting  (Fig.  145).  With  the 
application  of  heat,  the  nitrate  is  decomposed,  and  the 
acid  distils  over  into  the  receiver.  The  change  is  thus 
shown : 

NaNO,  +  H2SO4  =  NaHSO4  +  HNOs. 

That  is,  one  molecule  of  sodic  nitrate  and  one  of  sulphuric 
acid  furnish  one  molecule  of  nitric  acid  and  one  of  hydro- 
sod  ic  sulphate. 

360.  Properties. — Nitric    acid   is    a   colorless,   mobile 
liquid,  of  1.52  specific  gravitjr,  fuming   in  contact   with 
the  air,  and  possessed  of  an  intensely  sour  taste  and  pe- 
culiar sweetish-nauseous  pungent  smell.     It  becomes  solid 
at  very  low  temperatures,  and  boils  at  86°  C.,  with  partial 
decomposition.  It  is  highly  corrosive,  and  stains  of  a  yellow 
color  the  skin,  nails,  and  many  other  animal  substances; 
it   is   therefore    used    to   produce   yellow   patterns    upon 
woolen  fabrics.     It  is  also  employed  for  etching  on  copper, 
for  assaying  or  testing  metals,  and,  by  dyers  and  calico- 
printers,  as  a  solvent  for  tin.     In  consequence  of  its  large 
proportion  of  oxygen,  it  corrodes  the  metals  with  great 
energy,   and    hence   is   the    most   powerful    of    oxidizing 
agents.     It  ignites  powdered  charcoal  and  oil  of  turpen- 
tine, and  oxidizes  phosphorus  so  rapidly  as  to  produce  an 
explosion. 

361,  A  mixture  of  chlorohydric  acid  with  nitric  acid 
constitutes  the  aqua  regia,  or  royal  water,  of  the  alchemists, 
so  named  from  the  power  it  possesses  of  dissolving  gold, 
the  "king  of  metals,"  a  property  due  to  the  presence  of 
chlorine,  which,  at  the  moment  of  its  formation,  attacks 
metals  with  great  energy.     The  proportions  for  the  mixt- 
ures are  four  measures  of  hydric  chloride  to  one  of  nitric 
acid. 


204  DESCRIPTIVE   CHEMISTRY. 

362.  Ammonic  Chloride  (NH4C1)  (Sal-ammoniac). — This 
substance  is  found  native  in  many  volcanic  regions,  in  the 
vicinity  of  burning  coal-mines,  and  in  guano-deposits. 

FIG.  146. 


Formation  of  Ammonic  Chloride. 

When  hydric  chloride  and  ammonia  are  brought  together, 
they  form  dense  white  clouds  of  sal-ammoniac,  as  may  be 
seen  in  Fig.  146.  The  reaction  is  expressed  thus  : 

NH,  +  HC1  NH4C1. 

Ammonia  Gas.  Hydric  Chloride.  Ammonic  Chloride. 

When  a  solution  of  ammonic  hydrate  is  neutralized  by 
hydric  chloride,  crystals  of  ammonic  chloride  are  produced, 
which  have  a  sharp  taste,  and  dissolve  in  thrice  their 
weight  of  cold  water.  Sal-ammoniac  is  chiefly  obtained 
by  neutralizing  the  ammoniacal  liquor  of  the  gas-works  by 
hydric  chloride.  On  evaporating  the  resulting  solution, 
the  salt  appears  in  the  form  of  the  tough,  fibrous  crystals 
of  commerce.  It  is  volatilized  by  heat.  Mixed  with  lime, 
which  decomposes  it  and  expels  the  ammonia,  it  is  used  in 
smelling-bottles. 

363.  Ammonic  Hydrate  (NH5O)  (Aqua  Ammonia). — 
This  compound  is  prepared  by  passing  ammonia  gas  (NHg) 
into  water,  which  absorbs  it  rapidly  to  the  extent  of  700 
times  its  own  volume.  The  gas  is  evolved  by  gently  heat- 


NITROGEN   AND   ITS  COMPOUNDS. 


205 


FIG.  147. 


ing  a  mixture  of  slacked  lime  and  sal-ammoniac,  and  pa&s- 
ing  it  through  a  series  of  bottles.  la  making  solutions  of 
the  absorbable  gases  several  difficulties  have  to  be  guarded 
against.  The  action  in  the 
evolution-flask  is  liable  to 
various  interruptions,  while 
the  water  present  in  the 
apparatus  rapidly  absorbs 
the  gas.  This  creates  a 
partial  vacuum,  and  the 
consequence  is,  that  the 
water  in  the  jar  flows  back 
into  the  flask,  thus  putting 
an  end  to  the  process  ;  also,  Wouifes  Bottles, 

if  the  gas  is  generated  fast- 
er than  it  is  absorbed,  there  arises  the  danger  of  an  explo- 
sion, unless  there  is  a  free  outlet  to  the  apparatus.     These 
dangers  are  obviated  by  the  arrangement  known  as  Woulfe's 
bottles  (Fig.  147). 

The  flask  in  which  the  gas  is  generated  is  provided  with 
a  safety  tube  which  serves  both  as  a  means  of  introducing 
a  liquid  and  as  a  protection  against  the  above-mentioned 
accidents.  When  the  liquid  is  poured  in,  a  portion  of  it  is 
retained  in  the  bend  of  the  tube,  acting  there  as  a  valve  to 
prevent  the  access  of  air  to  the  flask.  Each  bottle  has  an 
upright  tubs  in  the  middle  neck  which  acts  as  a  safety- 
tube,  allowing  the  air  in  case  of  a  vacuum  to  pass  in,  or 
the  liquid  in  flow  out,  if  the  pressure  of  the  gas  becomes 
too  great.  The  other  tubes  serve  to  connect  the  bottles 
with  the  flask  and  with  each  other. 

364.  Properties. — Ammonic  hydrate  is  a  colorless,  trans- 
parent liquid,  of  0*85  specific  gravity,  with  the  pungent 
odor  of  ammonia,  and  a  sharp,  burning  taste.  As  usually 
met  with,  it  is  rarely  a  definite  compound,  being  liable  to 
contain  either  more  water  or  gas  than  the  above  formula 
implies.  A  saturated  solution  freezes  between  —38°  and 


206  DESCRIPTIVE   CHEMISTRY. 

—41°  C.,  forming  shining,  flexible,  needle-shaped  crystals. 
It  boils  at  130°  F.,  but  is,  at  the  same  time,  decomposed 
with  evolution  of  ammonia.  The  graphic  formula  of  am- 
monic  hydrate  is  (HJsN-O-H.  The  single  atom  of  hydro- 
gen which  is  linked  to  the  one  oxygen-atom  is  replaceable 
by  negative  radicles ;  the  resulting  compounds  are  termed 
ammoniacal  salts.  These  salts  are  remarkable  as  being 
isomorphous  with  certain  potassic  compounds,  and  when 
the  formulas  of  any  two  of  these  isomorphous  salts  are 
compared,  it  is  found  that  the  atomic  group  H4N  exactly 
corresponds  in  function  to  the  radical  potassium.  Thus  in 
comparing  the  formulas  of  the  two  well-known  isomorphous 
salts — 

Potash-alum         K         A1S2O8  +  12H2O,  and 
Ammonia-alum    H4N    A1S3O8  +  12HaO, 

we  readily  observe  this  analogy.  On  account  of  this  re- 
markable fact,  it  has  been  assumed  that  the  atomic  group, 
H4N,  or  its  double  molecule  (H8N2),  must  be  very  similar 
in  character  to  potassium,  and  possessed  of  metallic  prop- 
erties. This  radical  has  been  named  ammonium. 

365.  Ammonic  Nitrate,  (H4N)  NO3,  is  formed  in  small 
quantities  during  thunder-storms,  and  is  sometimes  con- 
tained in  rain-water.     Ammonic  sulphate,  (H4N)3  SO4,  is  a 
valuable  fertilizer.     Several  ammonic  carbonates  are  known, 
and  the  commercial    ammonic    carbonate,   when   purified, 
constitutes  the  volatile  salts,  or  smelling-salts,  of  the  shops. 

§  2.  Phosphorus  and  its  Compounds. 

PHOSPHORUS. — Symbol,  P.  Atomic  Weight,  31 ;  Molecular  Weight,  124; 
Molecular  Volume,  2 ;  Quantivalence,  I.,  III.,  V. ;  Specific  Gravity, 
1.82. 

366.  Distribution, — Phosphorus    is    found    in    Nature 
chiefly  in  combination  with  calcium.     It  is  a  never-failing 
constituent  of  the  plants  used  by  man  and  the  domestic 
animals.     It  is  an  equally  important  ingredient  of  animal 


PHOSPHORUS  AND   ITS  COMPOUNDS.  207 

skeletons,  which  owe  their  strength  to  calcic  and  magnesic 
phosphates,  while  it  also  exists  in  other  combinations  in 
the  blood,  flesh,  milk,  and  other  tissues,  and  secretions  of 
animals.  Phosphorus  exists  in  several  allotropic  states. 
Ordinarily,  it  is  a  white  solid,  with  a  faint-yellow  tinge, 
and  almost  transparent;  when  exposed  to  light  under 
water,  it  gradually  becomes  white,  opaque,  and  scaly. 
Exposed  to  direct  sunlight  under  water,  phosphorus  be- 
comes covered  with  a  red  coating,  and  the  same  modifica- 
tion is  formed  when  ordinary  phosphorus  is  heated  to  a 
temperature  below  250°  C.,  in  a  gas  which  has  no  action 
upon  it.  None  of  the  modifications  are  found  native. 

367.  Ordinary  Phosphorus  (P4).— This  interesting  body 
was  discovered  in  1669  by  Brandt,  who  obtained  it  by  dis- 
tilling the  residue  of  evaporated  urine  with  charcoal.     Most 
of  the  phosphorus  of  commerce  is  obtained  by  the  decompo- 
sition of  the  bones  of  animals,  which  consist  largely  of  calcic 
phosphate  (Ca3P3O8).     The  bones  are  first  burned,  and,  the 
organic  matter  being  consumed,  they  are  reduced  to  pow- 
der and  soaked  in  concentrated  sulphuric  acid.     This  de- 
composes the  phosphate,  with  formation  of  insoluble  calcic 
sulphate,  and  soluble  acid    calcic   phosphate  (CaH4PaO8). 
The  solution  of  this  compound,  after  being  separated  from 
the  sulphate,  evaporated  to  sirupy  consistence,  mixed  with 
charcoal,  and  heated  in  an  iron  pot,  is  distilled  at  a  bright- 
red  heat.     The  carbon  unites  with  the  oxygen,  liberating 
the  phosphorus,  which  rises  in  vapor,  and  is  condensed  in 
water  in  the  shape  of  yellow  drops.     These  are  melted 
under  water  and  forced  into  tubes,  thus  forming  the  ordi- 
nary stick-phosphorus. 

368.  Properties. — Phosphorus  is  a  soft,  colorless,  half- 
transparent,  waxy  solid,  so  extremely  inflammable  that  it 
takes  fire  in  the  open  air  by  the  heat  of  the  slightest  fric- 
tion, and  burns  with  great  violence,  emitting  a  brilliant 
flame,  and  dense,  white  fumes  of  phosphoric   pentoxide. 
If  quietly  exposed  to  the  air,  it  undergoes  slow  oxidation, 


208  DESCRIPTIVE   CHEMISTRY. 

emitting  white  vapors  of  a  garlic  odor  and  shines  in  the 
dark,  whence  its  name,  phosphorus,  bearer  of  light.  It  must 
he  handled  with  caution,  as  the  burns  it  produces  are  deep 
and  difficult  to  heal.  It  is  insoluble  in 
water ;  partially  soluble  in  ether,  but 
dissolves  readily  in  carbonic  disulphide 
and  various  oils.  It  melts  at  44°  C.,  form- 
ing a  viscid,  oily  liquid.  In  warm  weath- 
er phosphorus  is  flexible,  and  may  be 
bent  without  breaking,  but  near  the  freez- 
ing-point of  water  it  becomes  brittle,  ex- 
hibiting a  cystalliue  fracture.  On  ac- 
count of  its  inflammability  it  is  kept  under  water.  It 
crystallizes  from  its  solution,  in  forms  of  the  monometric 
system  (Fig.  148).  Solutions  of  phosphorus,  as  well  as 
the  solid  itself,  are  luminous  in  the  dark.  Phosphorus  is 
a  violent  poison.  The  chief  use  of  this  substance  is  in  the 
manufacture  of  friction-matches ;  and  vast  quantities  are 
consumed  in  this  way  among  all  civilized  nations. 

369.  Red  Phosphorus.— This  substance  may  be  obtained 
by  exposing  ordinary  phosphorus  to  sunlight,  or  heating 
it  to  near  its  boiling-point  in  an  atmosphere  free  from  oxy- 
gen.    As  thus  prepared,  red  phosphorus,   also  known  as 
amorphous  phosphorus,  is  a  red  powder,  of  about  2.18  spe- 
cific gravity,  much  less  fusible  than  ordinary  phosphorus, 
but  reverting  into  the  latter  at  about  260°  C.     It  exhales  no 
vapor  or  odor ;  oxidizes  but  very  slowly  in  the  air,  does 
not  change  oxygen  into    ozone,  is  chemically  indifferent, 
may  be  handled  with  impunity,  or  carried  exposed  in  the 
pocket,  and  is  not   poisonous.      Phosphorus    forms    three 
compounds  with  hydrogen,  but  only  one  is  of  importance 
to  the  ordinary  student. 

370.  Hydric  Phosphide  (H3P)  (Phosphu retted  Hydro- 
gen).— This  is  a  colorless  gas,  with  a  very  offensive  odor, 
like  rotten  fish.     It  is  found  in  Nature,  being  produced  in 
small  quantities  by  the  decay  of  animal  matter,  and  ap- 


PHOSPHORUS   AND   ITS   COMPOUNDS. 


2C9 


pears  to  be  the  cause  of  the  will  o'  the  wisp.  It  may  be 
prepared  by  heating  small  fragments  of  phosphorus  with 
a  strong  solution  of 
potash  in  a 
The  end  of 
dips 
and, 


FIG.  149. 


Wreaths  of  Flaine. 


caustic 
retort. 

the  retort-tube 
beneath  water, 
as  the  gas  passes  out 
in  bubbles,  it  rises  to 
the  surface  and  takes 
fire  spontaneously. 
If  some  pieces  of  cal- 
cic phosphide  are  thrown  into  a  glass  of  water,  the  same 
thing  takes  place.  Double  decomposition  with  the  water 
produces  hydric  phosphide,  which  ignites  at  the  surface 
and  forms  beautiful  wreaths  of  vapor  (Fig.  149).  Pure 
hydric  phosphide  (H3P)  is,  however,  not  spontaneously 
inflammable,  this  property  being  due,  in  this  case,  to  the 
admixture  of  a  minute  quantity  of  a  liquid  compound 
(H4P2).  It  is  poisonous.  In  many  cases  the  combining 
weights  and  the  unit-volume  weights  are  identical.  But 
the  atomic  weight  of  phosphorus  is  31 ;  while  the  specific 
gravity  of  its  vapor  has  been  found  to  be  62.1.  The  volu- 
metric composition  of  hydric  phosphide  will  be  readily 
understood  by  reference  to  the  accompanying  diagram  : 


H 
1 


H 
1 

"H 

i 


}>  + 


PH334 


210 


DESCRIPTIVE   CHEMISTRY. 


FIG.  150. 


Combustion  of  Phosphorus. 


371.  Phosphoric  Pentoxide  (PaO&).-~When  phosphorus 

is  burned  in  dry  oxygen  (Fig1. 
150),  the  dense,  white  vapors 
which  are  formed  condense 
upon  the  glass  in  snow-like 
flakes.  This  is  phosphoric 
pentoxide.  Tt  has  a  power- 
ful attraction  for  moisture, 
absorbing  it  from  the  air,  or, 
if  brought  into  contact  with 
water,  seizing  it  with  such 
violence  as  to  emit  a  hissing 
sound.  By  the  union  of  phosphoric  pentoxide  with  water, 
there  are  formed  three  distinct  acids:  meta-phosphoric 
acid  (HPO3),  pvro-phosphoric  acid  (H4P2O7),  and  ortho- 
phosphoric  acid  (H3PO4). 

§  3.  Arsenic  and  its  Compounds. 

ARSENIC. — Symbol,  As.    Atomic  Weight,  75;  Quantivalenee,  III.  and  V. 
Molecular  Weight,  300 ;  Molecular  Volume,  2  ;  Specific  Gravity,  5.79. 

372.  Arsenic. — This  element  is  found  native,  but  most 
of  the  arsenic  of  commerce  is  obtained  by  the  decomposi- 
tion of  the  arsenides.     The  compounds  are  heated  in  retorts 
of  earthen-ware ;  the  arsenic  sublimes  and  collects  in  iron 
tubes  and  earthen  receivers. 

Arsenic  is  a  brittle  metal,  of  a  steel-gray,  or  nearly 
white  color.  The  coarse,  gray  powder,  sold  under  the 
name  of  "  fly-poison,"  or  "  cobalt,"  is  an  impure  arsenic. 
When  arsenic  is  heated  in  a  close  vessel  to  356°  F.,  it  vola- 
tilizes without  fusion,  giving  off  a  dense,  colorless  vapor, 
having  the  peculiar  odor  of  garlic,  and  corresponding  to 
the  formula  As4.  If  heated  in  the  open  air  it  takes  fire, 
burning  with  a  blue  flame,  with  formation  of  arsenic  tri- 
oxide.  Tt  is  highly  poisonous. 

373.  Hydric   Arsenide    (H8As.)    (Arseniuretted   Hy- 


ARSENIC   AND   ITS  COMPOUNDS.  211 

drogeri). — This  gas  may  be  formed  by  decomposing  an 
allov  of  arsenic  and  iron  with  dilute  sulphuric  acid,  or  by 
introducing  a  solution  of  arsenic  into  a  FIG.  isi. 

flask  in  which  hydrogen  is  being  evolved. 
It  burns  with  a  bluish  white  flame,  is  high- 
ly poisonous,  and  of  a  disgusting  odor. 
The  formation  of  this  gas  is  used  for  the 
detection  of  arsenic  by  Marsh's  test. 
Fig.  151  shows  the  form  of  an  appa- 
ratus which  answers,  in  a  rough  way, 
very  well  for  this  purpose.  Bits  of  zinc 
and  a  little  water  are  placed  in  the 
vessel,  which  is  provided  with  a  cork 
through  which  a  tube  is  inserted.  Sul- 
phuric acid  is  now  poured  in  through  the 
funnel-tube,  and  the  evolution  of  hydro- 

,  ,,         A ,  .     ,          ,  Marsh's  Test. 

gen  commences.  Atter  the  air  has  been 
completely  expelled  from  the  flask,  the  gas  may  be  lighted 
at  the  jet.  If  the  solution  containing  arsenic  be  now 
poured  in  through  the  funnel-tube,  the  color  of  the  flame 
immediately  changes,  and  a  cold,  white  surface,  held  so  as 
to  cut  the  flame  in  half,  is  stained  with  a  black  or  brown 
spot  by  the  deposition  of  metallic  arsenic.  Antimony 
produces  a  similar  effect,  but  a  solution  of  calcic  or  sodic 
hypochlorite  dissolves  the  arsenical  stain,  leaving  that 
made  by  antimony  unchanged.  This  is  a  very  delicate 
test,  but  great  care  should  be  taken  that  the  sulphuric  acid 
and  zinc  do  not  contain  any  previous  traces  of  arsenic.  It 
is  estimated  that  g()^00  of  a  grain  of  arsenious  oxide  in  one 
hundred  grain  measures  of  the  solution  may  be  detected 
by  this  test. 

374.  Arsenic  Trioxide  (As2O3)  (Arsenious  Acid). — 
This  compound  occurs  native,  but  is  also  prepared  on  a 
large  scale  by  roasting  certain  ferric  arsenides,  and  other 
arsenical  ores.  Thus  obtained,  it  constitutes  the  well- 
known  white  arsenic  or  ratsbane  of  commerce,  ,a  white 


212  DESCRIPTIVE   CHEMISTRY. 

solid  body,  capable  of  existing  in  three  isomeric  forms.  It 
is  soluble  in  about  ten  parts  of  hot  water,  the  solution 
having  a  slightly  sweetish  taste,  and  acid  reaction.  It 
also  dissolves  readily  in  hot  hydric  chloride,  and  in  solu- 
tions of  the  alkaline  arsenites.  It  is  used  in  dyeing  and 
calico-printing,  in  glass-making,  and  for  the  preparation 
of  arsenical  soap,  which  is  employed  for  preserving  stuffed 
animals.  Though  a  violent,  corrosive  poison,  it  is  used  in 
medicine ;  its  most  effectual  antidotes  are  the  moist  hy- 
drated  ferric  oxide  and  caustic  magnesia.  Ortho-arsenic, 
acid  (H3AsO4)  is  formed  by  oxidizing  arsenious  oxide  by 
means  of  nitric  acid.  It  has  strongly  acid  properties, 
decomposing  the  carbonates  with  effervescence.  Arsenic 
disulphide  (As2S2)  has  been  known  since  very  remote 
times,  and  is  found  native  as  realgar,  a  mineral  crystal- 
lizing in  translucent,  oblique,  rhombic  prisms,  of  beau- 
tiful orange-yellow,  or  ruby-red,  color.  It  is  produced 
artificially,  is  used  as  a  pigment,  and  in  the  preparation 
of  the  pyrotechnical  mixture  known  as  "Bengal  white- 
light."  Arsenic  trisulphide  (As2S3),  familiarly  known 
as  "orpiment,"  is  found  native,  but  is  also  prepared 
artificially.  It  is  a  bright-yellow  substance,  and  is  used 
in  dyeing  to  reduce  indigo,  and  also  in  the  prepara- 
tion of  "rusma,"  a  paste  employed  to  remove  the  hair 
from  skins. 

§  4.  Antimony  and  Bismuth. 

ANTIMONF.— Symbol,  Sb.  (Stibium).  Atomic  Weight,  122;  Quantivalence, 
III.  and  V. ;  Molecular  Weight,  488  (?);  Molecular  Volume,  2;  Spe- 
cific Gravity,  6.78. 

375.  Antimony  is  found  native,  though  most  of  the 
antimony  of  commerce  is  obtained  from  the  trisulphide 
(Sb2S3).  It  exists  in  two  modifications  ;  ordinarily  it  is  a 
brittle,  brilliant,  bluish-white  metal,  crystallizing  in  rhom- 
bohedrnns.  The  other  form  is  obtained  by  electrolysis,  and 


ANTIMONY  AND   BISMUTH.  213 

has  a  specific  gravity  of  5.78.  When  struck  or  heated  it 
suddenly  reverts  to  the  previous  modification,  with  great 
evolution  of  heat.  Antimony  melts  at  450°  C.,  and  va- 
porizes at  a  white  heat.  Heated  in  the  air  it  burns  with  a 
white  flame.  The  alloys  of  antimony  are  of  great  use  in 
the  arts.  Of  these,  type-metal,  an  alloy  of  lead  and  anti- 
mony, is  the  most  important.  The  detection  and  separa- 
tion of  arsenic  and  antimony  is  a  subject  cf  much  impor- 
tance as  both  alike  exhibit  poisonous  characters  and  similar 
reactions  (373).  Stibic  trioxide  (Sb2O3)  is  produced  when 
metallic  antimony  burns  in  the  air.  It  is  white,  crystal- 
line, isomorphous  with  arsenic  trioxide,  sparingly  soluble  in 
water.  It  is  used  as  a  pigment  in  place  of  white  lead, 
and  gives  rise  to  the  salts  of  antimony  so  much  used 
in  medicine.  Stibic  trisulphide  (Sb2S3)  is  employed  in 
veterinary  surgery,  in  pyrotechny,  and  in  the  preparation 
of  the  percussion  pellets  used  in  the  cartridges  of  the 
Prussian  needle-gun. 

BISMUTH. — Symbol,  Bi.    Atomic  Weight,  210 ;  Quantivalence,  III.  and  V. ; 
Specific  Gravity,  9.8. 

376.  Bismuth. — This  metal,  which  has  long  been  known, 
is  found,  in  the  metallic  state,  in  veins  in  gneiss,  clay, 
slate,  and  other  crystalline  rocks,  chiefly  in  Saxony  and 
Bohemia.  The  commercial  material  is  derived  from  the 
native  metal  by  purification.  It  is  hard,  brittle,  reddish- 
white  in  color,  and  crystallizes  from  fusion  in  rhombohe- 
drons.  It  melts  at  264°  C.,  and  on  solidifying  expands 
one  thirty-second  of  its  bulk.  It  is  volatile  at  high  tem- 
peratures. Heated  in  the  air  it  burns  with  a  bluish  flame, 
giving  rise  to  yellow  fumes.  Bismuth  is  used  in  the  arts 
alloyed  with  other  metals,  and  its  compounds  are  used  in 
medicine  and  as  pigments. 


DIVISION  II.-ARTIAD  ELEMENTS. 


CHAPTER    XVI. 

§  1.    Oxygen  and  its  Compounds. 

OXYGEN. — Symbol,  0.     Atomic  Weight,  16;  Quanti valence,  II.;  Molecu- 
lar Weight,  32  ;  Molecular  Volume,  2  ;  Specific  Gravity,  1.1056. 

377.  Modifications  of  Oxygen. — Oxygen  is  known  to  us 
in  three  modifications,  consisting,  apparently,  of  one,  two, 
and  three  atoms  of  the  radical  bearing   the  same  name. 
The  second,  only,  of  these  is  generally  termed  oxygen ; 
the  molecule  containing  three  atoms  of  the  radical  oxygen 
is  known  as    ozone,   and  the   body  containing   only  one 
atom  as  antozone. 

378.  Oxygen  (Ordinary  Modification)  (O2). — This  gas 
was  discovered  in  1774,  by  Dr.  Priestley,  and  the  following 
year  it  was  discovered,  independently,  by  Scheele.      Its 
discovery  was  also  claimed  by  Lavoisier,  who,  in  1781, 
gave  it  the  name  oxygen,  from  two  Greek  words,  meaning 
acid-former.     This  has  been  justly  pronounced  the  capital 
discovery  of  the  last  century,  rivaling  in  importance  the 
great   discovery  of  gravitation,  by  Newton,  in  the   pre- 
ceding century.     It  formed  one  of  the  great  eras  in  the 
progress    of   human    knowledge;    it    put  an    end   to   old 
theories,  laid  the  foundation  of  modern  chemical  science, 
and   furnished   the   master-key  by  which    man    has   been 
enabled  to  open  the  mysteries  of  Nature.     But  while  the 
discovery  of  gravitation  is  unsurpassed  in  grandeur,  that 
of  oxygen  is  far  more  vitally  linked  with  the  course  of 
earthly  affairs. 


OXYGEN  AND   ITS   COMPOUNDS.  215 

379.  Of  its  vast  practical  consequences,  Professor  Lie- 
big  observes :    "  Since  the  discovery  of  oxygen,  the  civil- 
ized world  has   undergone  a  revolution  in    manners   and 
customs.      The  knowledge  of  the  composition  of  the  at- 
mosphere, of  the  solid  crust  of  the  earth,  of  water,  and 
of  their   influence  upon   the   life  of  plants   and  animals, 
was   linked   with    that    discovery.      The    successful   pur- 
suit  of   innumerable   trades   and  manufactures,  the   prof- 
itable  separation  of    metals   from    their   ores,  also  stand 
in   the    closest    connection    therewith.      It   may   well   be 
said  that  the  material  prosperity  of  empires  has  increased 
manifold  since  the  time  oxygen  became  known,  and  the 
fortune  of  every  individual  has  been  augmented  in  pro- 
portion." 

380.  Occurrence. — Oxygen  is  the  mos.  abundant  ele- 
ment in  Nature.     It  is  of  universal  distribution  through 
our  atmosphere,  forming  one-fifth  part  of  the  air  we  breathe. 
The  total  quantity  contained  in  the  atmosphere  has  been 
computed  to  be  about  1,178,158,000,000,000  tons,  which, 
if  forming  a  separate  layer  of  uniform  density  upon  the 
earth's  surface,  would  be  one  mile  deep.     It  constitutes 
eight-ninths  of  water  by  weight,   besides   being   a  con- 
stituent  of  nearly  all   the  rocks  of  the  globe;   and   en- 
tering largely  into  the  organized  structure  of  plants  and 
animals. 

381.  Preparation. — Oxygen  may  be  procured  in  many 
ways.     Mercuric  oxide  and  manganic  dioxide  readily  yield 
it  when  they  are  exposed  to  a  high  temperature.     It  can 
be  obtained  in  larger  quantity,  and  very  pure,  from  potas- 
sic  chlorate.     Two  hundred  grains  of  the  salt,  or  about 
fourteen  grammes,  are  placed  in  a  glass  flask,  which  is  fitted 
tightly  with  a  cork,  containing  a  glass  tube,  bent  so  as  to 
dip  under  the  shelf  of  the  pneumatic  trough  (Fig.  152). 
The  flask  is  heated,  and  the  chlorate  gives  off  more  than  a 
third  of  its  weight  of  gas.     This  salt  consists  of  potassium, 
chlorine,  and  oxygen,  and  in  the  change  the  whole  of  the 

10 


216 


DESCRIPTIVE   CHEMISTRY. 


oxygen    is   disengaged,   potassic   chloride   remaining    be- 
hind. 

2KC1O3  =  2KC1  +  3O2. 

The  decomposition  of  the  chlorate  is  much  facilitated  by 
mixing  with  it  one-fourth  its  weight  of  cupric  oxide,  or 

FIG.  152. 


Generating  Oxygen  Gas. 

manganic  dioxide,  thoroughly  dried.  These  substances 
take  no  active  part  in  the  change,  but  seem  to  aid  the 
decomposition  by  simple  presence  (catalysis). 

382.  Properties. — Oxygen  is  a  transparent,  colorless, 
tasteless,  inodorous  gas.  It  is  about  ^  heavier  than  at- 
mospheric air.  It  has  never  been  condensed  into  a  liquid. 
The  refractive  power  of  oxygen  compared  with  that  of  air 
as  unity  is  0.8616.  It  possesses  magnetic  properties,  but 
loses  them  at  a  high  temperature.  Oxygen  is  slightly  sol- 
uble in  water,  100  volumes  of  which  absorb  about  4J  of 
the  gas. 

Oxygen  is  perfectly  neutral,  possessing  neither  acid  nor 
alkaline  qualities,  but,  though  apparently  the  very  type  of 
passiveness,  this  substance  is  endowed  with  the  most  in- 
tense power.  The  two  atoms  of  the  radicle,  which  together 


OXYGEN  AND   ITS   COMPOUNDS. 


217 


FIG.  153. 


Taper  in  Oxygen. 


form  a  molecule  of  oxygen  gas,  are  held  by  but  feeble 
attraction,  and  are  easily  severed,  when  they  enter  into 
new  and  firmer  combinations. 

383.  Combustion  in  Oxygen. — The   oxygen   of  the   air 

(about  one-fifth  of  its  weight)  is  equal- 
ly diffused  throughout  it.  All  com- 
bustion in  the  open  air  is  the  result  of 
the  action  of  oxygen.  It  has  a  power- 
ful affinity  for  the  elements  of  which 
fuel  is  composed,  and  unites  with  them 
with  such  violence  as  to  give  rise  to 
the  heat  and  light  of  our  ordinary 
fires.  All  substances  which  burn  in 
air,  burn  in  pure  oxygen  with  greatly 
increased  brilliancy.  If  the  flame  of 
a  taper  (Fig.  153)  be  extinguished, 

and  a  single  spark  remain  upon  the  wick,  on  plunging  it 

into  a  jar  of  pure  oxy- 
gen, it  will  be  relighted 

and  burn  with  extreme 

vividness  ;  and  this  may 

be  repeated  many  times 

in  the  same  vessel  of 

gas.      The  combustion 

of  a  splinter  of  wood  is 

brilliant,  and  a  piece  of 

bark  charcoal  glows  and 

scintillates  in  the  most 

beautiful  manner. 

384.  Substances 
usually  considered    in- 
combustible   also  burn 
violently  in  oxygen.     If 

*  n  .  Combustion  of  Iron  in  Oxygen. 

a  piece  ot  hne  iron  wire 

(or,  better  still,  a  steel  watch-spring)  be  coiled  into  a  spiral 

and  then  tipped  with  sulphur,  ignited  and  introduced  into 


FIG.  154. 


218 


DESCRIPTIVE   CHEMISTRY. 


FIG.  155. 


FIG.  156. 


a  jar  of  oxygen,  it  burns  with  dazzling  brilliancy  and  splen- 
did corruscations  (Fig.  154).  Occasionally  globules  of 
white-hot  iron  fuse  into  the  glass  even  through  an  inch 
depth  of  water.  If  a  jar  of  oxygen  be  inverted  over  a  stand 
upon  which  there  is  a  little  burning  sulphur,  a  beautiful 
blue  light  is  emitted,  and  the  fumes  produced  circulate 

round  in  curious  rings  (Fig.  155). 

If  phosphorus  be  burned  in  the 

same  manner,  a  blinding  flood  of 

light  is   produced,   accompanied 

by    great    heat    (Fig.   156).     In 

all   these   cases,  the    effects    are 

due  simply  to  the  union  of  0x3^- 

gen  with  the  burning  body,  and, 

could  we  have  weighed  them  be- 

fore  the  experiment,  and  the  prod- 
ucts of  combustion  afterward,  they  would  have  been  found 
precisely  equal. 

385.  Eremacausis. — The   cause  of  decay  in  vegetable 
and   animal    substances    is   the    action   of  oxygen,  which 
breaks  them  up  into  simpler  and  more  permanent  com- 
pounds.    This  slow  combustion  is  called  by  Liebig  erema- 
causis.     Oxidation  is  also  the  grand  process  by  which  the 
earth,  air,  and  sea,  are  purified  from  contaminations ;  nox- 
ious vapors  and  pestilential  effluvia  being  destroyed  by  a 
process  of  burning,  more  slow  indeed,  but  as  real  as  if  it 
took  place  in  a  furnace.     The  offensive  impurities  which 
constantly  flow  into  rivers,  lakes,  and  oceans,  as  well  as 
the  decaying  remains  of  the  living  tribes  which  inhabit 
them,  are  perpetually  oxidized  by  the  dissolved  gas,  and 
the  water  thus  kept  pure  and  sweet.     In  this  way  waters 
that  have,  become  foul  and  putrid  are  purified  and  sweet- 
ened by  exposure  to  the  action  of  air.     This  effect,  how- 
ever, is  largely  dependent  upon  the  presence  of  ozone. 

386.  Relation  of  Oxygen  to  Life. — Oxygen  is  the  uni- 
versal supporter  of  respiration,  and  hence,  as  this   is  the 


OXYGEN   AXD   ITS   COMPOUNDS.  219 

most  important  of  the  vital  processes,  it  is  the  immediate 
supporter  of  life.  From  this  circumstance  it  was  first 
known  as  vital  air.  An  animal  confined  in  a  given  bulk 
of  common  air,  having  consumed  its  oxygen,  dies.  If  im- 
mersed in  pure  oxygen,  it  lives  much  longer,  but  the  effect 
is  too  powerful — over-action,  fever,  and  in  a  short  time 
death,  are  the  result.  As  the  introduction  of  oxygen  is  the 
prime  physiological  necessity  of  animal  life,  the  mechanism 
of  all  living  beings  is  constructed  with  reference  to  this 
fact.  The  lungs  of  the  higher  races,  the  spiracula  of  in- 
sects, and  the  gills  of  fishes,  are  all  adapted  to  the  same 
purpose — the  absorption  of  oxygen,  either  from  the  air  or 
water.  The  animal  organism  is  chiefly  composed  of  com- 
bustible constituents,  and  we  introduce  this  wonderful 
element  incessantly,  day  and  night,  from  birth  to  death, 
that  it  may  perform  its  chemical  work.  The  animal  body 
is  an  oxidizing  apparatus,  in  which  the  same  changes  occur 
that  take  place  in  the  flame,  only  in  a  lower  degree,  and  a 
more  regulated  way.  Every  organ,  muscle,  nerve,  and 
membrane,  is  wasted  away,  burnt  to  poisonous  gases  and 
ashes,  and  thrown  from  the  system  as  dead  and  dangerous 
matter.  If  these  constant  losses  are  not  repaired  by  the 
due  supply  of  food,  emaciation,  decay,  and  finally  death 
ensue.  Starvation  is  thus  unimpeded  oxidation — slow 
burning  to  death. 

387.  Ozone  (O3). — When  electric  sparks  are  passed 
through  dry  air,  a  peculiar  odor  is  perceived,  which  has 
been  called  the  "  electrical  smell."  There  was  much  doubt 
about  the  cause  of  it,  until  the  investigations  of  Schonbein, 
and  of  Marignac,  and  De  la  Rive,  showed  that  it  was  due  to 
an  allotropic  form  of  oxygen.  From  its  peculiar  odor,  its 
discoverer  named  it  ozone.  In  Nature  this  modification  of 
oxygen  is  found  principally  during  and  after  thunder- 
storms; but  the  quantity  contained  in  the  atmosphere 
varies  considerably,  and  is  always  small.  Winds  blowing 
from  the  sea  are  said  to  contain  more  of  it  than  those 


220  DESCRIPTIVE   CHEMISTRY. 

which  sweep  over  large  tracts  of  land.  Oxygen  may  be 
converted  into  ozone  not  only  by  electricity,  but  in  various 
other  ways.  Thus,  when  a  spiral  of 
platinum  wire  is  heated  in  air,  or  when 
light  acts  upon  some  essential  oils,  in 
contact  with  air,  ozone  is  formed.  If 
a  piace  of  phosphorus  be  placed  in  a 
jar,  and  partially  covered  with  water, 
its  slow  oxidation  will  soon  produoe 
ozone.  Or,  if  we  place  a  little  ether  in 
an  open  vessel,  and  then  introduce  into 
Preparation  of  Ozone.  its  vapor  a  moderately  heated  glass  rod 

(Fig.  157),  ozone  promptly  appears. 
388,  Properties. — In  most  of  its  physical  properties 
ozone  resembles  the  ordinary  modification  of  oxygen.  It 
differs  from  it  in  possessing  a  powerful  odor,  somewhat 
resembling  dilute  chlorine  gas.  Its  molecular  weight  is 
48,  and  its  density  24.  It  is  soluble  only  in  oil  of  turpen- 
tine. The  most  remarkable  property  of  ozone  is  its  power- 
ful oxidizing  action.  In  fact,  it  is  oxygen  greatly  intensi- 
fied in  activity.  It  corrodes  metals  upon  which  ordinary 
oxygen  could  not  act,  for  example,  silver;  it  quickly 
bleaches  colors,  which  are  comparatively  permanent  in  the 
air;  it  deodorizes  tainted  flesh,  destroying  its  effluvium 
instantljT,  and  carries  woody  fibre  in  a  short  time  through 
a  course  of  decomposition,  which,  with  common  oxygen, 
would  require  years.  It  decomposes  potassic  iodide,  set- 
ting the  iodine  free.  Free  iodine  combines  with  starch, 
turning  it  blue ;  therefore,  a  test  of  ozone  is  made  by  soak- 
ing slips  of  paper  in  a  mixture  of  starch  and  potassic  iodide. 
The  slightest  trace  of  ozone  turns  it  immediately  blue. 
Prepared  paper,  exposed  for  a  few  minutes  to  the  open  air, 
will  frequently  turn  blue,  which  is  supposed  to  be  due  to 
the  presence  of  ozone.  It  is  probable  that  it  is  generated 
on  a  large  scale  in  the  atmosphere,  and  that  it  subserves  a 
high  purpose  in  the  economy  of  the  globe  as  a  purifier  of 


OXYGEN  AND  ITS  COMPOUNDS.  221 

the  air,  and  hastener  of  decay.  Ozonized  air  irritates  the 
respiratory  organs,  and  a  minute  quantity  kills  a  rabbit. 
At  a  temperature  of  290°  C.,  ozone  is  reconverted  into 
ordinary  oxygen. 

389,  Antozone  (O,). — The  existence  of  this  substance 
is  yet  somewhat  doubtful.     It  is  supposed  to  be  produced, 
together  with  ozone,  by  the  action  of  the  silent  electric 
discharge   upon  oxygen.     On  passing  the  electrized  gas 
through  a  solution  of  potassic  iodide,  the  ozone  is  absorbed, 
and   the   antozone   mixed    with   the   excess   of  unaltered 
oxygen  remains.     When  this  is  passed  through  water  it 
forms  a  peculiar  dense  mist,  which,  collected  by  itself,  dis- 
appears after  a  little  time,  depositing   only  pure  water. 
Antozone  is  reconverted  into  ordinary  oxygen,  under  the 
same    conditions    as    ozone,   but    the   reconversion   takes 
place  more  readily  in  the  presence  of  the  latter.      Ant- 
ozone has  an   odor   similar  to  ozone,  but  is   much  more 
repulsive. 

The  molecule  of  ordinarv  oxygen  is  regarded  as  con- 
stituted according  to  the  graphic  formula  O=O.  As  the 
density  of  ozone  is  to  that  of  ordinary  oxygen  as  3  :"  2,  the 
ozone-molecule  is  assumed  to  be  made  up  of  three  atoms  of 
the  radicle  oxygen.  When  two  molecules  of  ordinary 
oxygen  are  ozonized,  three  of  the  four  constituent  atoms 
combine  to  form  ozone.  It  is,  therefore,  held  that  ant- 
ozone consists  of  the  one  remaining  atom.  The  molecular 
and  graphic  formulas  of  the  three  forms  of  oxygen  exhibit 
the  following  relations : 

Antozone.  Oxygen.  Ozone. 

Molecular,  Ol  O2  O3 

A 

Graphic,  O>  OO  O-O. 

390.  Hydric  Oxide  (HQO),  Water.— Of  the  importance 
of  water  in  the  economy  of  Nature  little  need  be  said ;  it  is 
obvious  to  all.     It  is  the  most  abundant  substance  that  we 


£2%  DESCRIPTIVE   CHEMISTRY. 

know,  and  it  seems  as  if  the  whole  scheme  of  Nature  were 
conformed  to  its  properties.  Turning  to  solid  ice,  or  ex- 
haling into  invisible  vapor,  its  changes  of  form  involve  the 
very  history  of  the  globe.  Rising  from  the  ocean,  con- 
densed upon  the  land,  and  flowing  back  again  to  the  sea, 
it  carries  on  in  its  circulation  the  grand  processes  of  the 
world.  Constituting  four-fifths  the  weight  of  the  vegetable 
kingdom,  and  three-fourths  that  of  the  animal,  it  is  the 
first  condition  of  all  organization,  and  by  innumerable 
transformations  and  decompositions  it  is  essential  to  the 
continuance  of  organic  life.  Nor  is  it  less  indispensable  in 
the  laboratory  of  the  chemist.  It  is  the  ready,  invaluable 
medium  of  a  thousand  operations,  and  is  involved  in  nearly 
every  chemical  process. 

391.  Production  of  Water.  —  If  hydrogen  is  generated 
in  a  jar  and  allowed  to  escape  through  a  fine 
tube  (Fig.  158)  into  the  air,  it  burns,  when  ig- 
nited, with  a  small,  steady  flame,  giving  out  but 
little  light,  though  producing  intense  heat.  In 
all  cases  where  hydrogen  is  burned  with  oxygen. 
water  is  the  product.  If  a  cold,  dry  glass  is  held 
over  the  jet,  it  is  quickly  covered  with  a  film  of 
dew,  which  rapidly  increases  to  drops  of  water. 
^e  gases  unite  to  form  steam,  which  then  con- 
denses into  the  liquid  state. 

Oxygen  and  hydrogen  burn  quietly  when  brought 
cautiously  in  contact  and  ignited,  but,  if  the  gases  are 
mixed,  before  ignition,  in  the  proportion  of  one  volume 
of  the  first  to  two  of  the  second,  a  violent  explosion  re- 
sults. Soap-bubbles,  if  blown  with  this  mixture  from  a 
bag  and  fired  with  a  candle,  detonate  like  a  pistol  (Fig. 


392.  Composition,  —  Water  is  a  compound  of  8  parts  by 
weight  of  oxygen  to  1  of  hydrogen,  or  by  bulk  1  of  oxy- 
gen to  2  of  hydrogen.  Its  composition  may  be  proved  in 
many  ways,  but  one  of  the  most  simple  is  to  throw  a 


OXYGEN   AND   ITS   COMPOUNDS.  223 

little  metallic  potassium  upon  its  surface.     The  metal  in- 
stantly decomposes  it,  seizing  upon  the  oxygen,  and  set- 
ting hydrogen  free  with  such  violence  as  to  produce  the 
vivid  combustion  of  the  latter  (Fig. 
159);  the  water  seems  set  on  fire.  FlG- 159- 

Water  is  also  decomposed  by  so- 
dium, iron,  zinc,  and  many  other 
metals ;  in  fact,  they  have  been  long 
classified  according  to  their  degrees 
of  power  in  this  respect.  In  num- 
berless operations  of  chemistry,  the 
elements  of  water  are  separated  and 
reunited,  and  the  same  thing  is  going 
on  perpetually  in  vegetable  and  ani-  Decomposing  Water, 
mal  organisms. 

But  the  composition  of  water  may  be  shown  in  the  most 
perfect  manner  by  sending  an  electric  current  through  a 
vessel  of  it  (Fig.  62),  as  already  described  (141).  The 
gases  are  set  free  in  the  exact  proportions  given  above, 
and,  if  mixed  together  and  ignited,  they  combine  with  a 
loud  and  sharp  explosion,  the  product  being  pure  water. 
The  composition  of  water  is  thus  demonstrated  by  both 
analysis  and  synthesis. 

393.  General  Properties. — Pure  water  is  a  transparent, 
tasteless,  inodorous  liquid.  It  is  but  very  slightly  con- 
densible— according  to  Regnault,  being  compressed  1-47 
millionth  of  its  bulk  for  each  atmosphere  of  pressure — and 
is  perfectly  elastic,  as  it  regains  its  full  dimensions  when 
the  pressure  is  removed.  It  evaporates  at  all  tempera- 
tures; boils  at  100°  C.  or  212°  F.,  and  freezes  at  0°  C.  or 
32°  F.  It  is  815  times  heavier  than  an  equal  bulk  of  air. 
An  imperial  gallon  weighs  70,000  grains,  or  just  10  Ibs. 
The  American  standard  gallon  of  pure  distilled  water  at 
the  maximum  density  weighs  58,972  grains.  In  thin  sheets, 
water  is  colorless,  but  when  viewed  in  thick  masses  it  has 
a  decided  tint.  Light  passed  through  fifteen  feet  of  pure 


224:  DESCRIPTIVE   CHEMISTRY. 

distilled  water  emerges  of  a  bright  and  delicate  blue-green, 
and,  by  augmenting  the  thickness,  the  color  is  deepened. 

394.  Snow  Crystals. — Water,  in  freezing,  crystallizes. 
The  aqueous  vapor  of  the  atmosphere,  condensed  by  cold 
in  winter,  or  at  great  heights  in  summer,  assumes  the  most 
beautiful  crystalline  forms — those  of  snow-flakes.  Perfect 
snow-flakes  are  six-sided  stars — modifications  of  an  hexa- 
gonal prism — which  shoot  out  an  infinity  of  delicate 
needles,  all  diverging  from  each  other  at  an  angle  of  60°. 
These  frozen  blossoms,  as  they  have  been  aptly  termed, 
are  seen  in  an  endless  variety  of  most  exquisite  forms,  a 
few  of  which  are  shown  in  Fig.  160. 

FIG.  160. 


Forms  of  Snow-Flakes. — (GLAISHER.) 

When  a  ray  from  the  sun  or  an  electric  lamp  is  made  to 
pass  through  a  block  of  pure  ice,  a  portion  of  the  heat  is 
arrested,  and  must,  of  course,  produce  change.  As  it  cannot 
warm  the  ice,  it  melts  it.  But  the  ice-particles  return  to  the 
liquid  state  in  definite  order,  and,  upon  examining  it  with 
a  magnifier,  the  ice  is  seen  to  be  filled  with  beautiful 
flower-like  figures.  These  consist  of  water,  but  as  the 


OXYGEN   AND  ITS  COMPOUNDS.  225 

liquid  formed  cannot  quite  fill  the  space  of  the  melted  ice, 
there  occurs  a  little  vacuum,  which  looks  like  a  globule  of 
burnished  silver  in  the  centre  of  the  flower. 

395.  Unequal  Expansion  of  Water. — This  liquid  con- 
tracts as  its  temperature  falls  from  the  boiling-point  till  it 
reaches  39°  F.,  when  it  remains  stationary  for  a  time.     It 
then   begins   to   expand,  and,  in    cooling   through    7°  to 
the  freezing-point,  it  reaches  the  same  volume  it  had  at 
48°.     The  point  of  greatest  contraction  is  called  the  maxi- 
mum density  of  water.     This  fact  is  of  great  importance 
in  Nature.     If  water  continued  to  contract  as  it  cooled,  it 
would  be  denser  and  heavier  at  the  freezing-point,  and, 
consequently,  sink.     Lakes  and  rivers  would  then  begin  to 
freeze  at  the  bottom  first,  and,  in  the  course  of  the  winter, 
would  become  solid  masses  of  ice ;  while  the  length  of  time 
required  to  thaw   them  would   greatly  prolong  the  cold 
season.     But  as  the  surface  stratum  of  water  approaches 
the  freezing-point  and  freezes,  it  expands,  and,  becoming 
lighter,  floats,  and  thus  the  coldest  water  and  ice  are  kept 
at  the  surface,  where,  as  they  are  almost  perfect  non-con- 
ductors of  heat,  they  protect  the  mass  of  water  below  from 
the  cold  above.      In   freezing,  water  expands  with  such 
power   as   to   burst   the   strongest   vessels.      Percolating 
the  minute  crevices  and  fissures  of  rocks  in  summer,  it 
freezes  in  winter,  and  expands  with  a  force  which  breaks 
the  solid  stones,  crumbling  them  into  soil  fit  for  the  sup- 
port of  vegetable  life. 

396.  Its  Specific  Heat.— The  great  specific  heat  of  water 
is  a  powerful  agency  in  controlling  climate.    It  is  four  times 
greater  than  that  of  air ;  that  is,  a  pound  of  water,  in  cool- 
ing one  degree,  would  warm  four  pounds  of  air  one  degree. 
But,  as  water  is  770  times  heavier  than  air,  it  is  obvious  that 
a  cubic  foot  of  water,  in  cooling  one  degree,  would  warm 
four  times  770  cubic  feet  of  air,  or  3,080  cubic  feet  one 
degree.     Hence,  the  vast  amount  of  heat  stored    up  in 
oceans  and   lakes,  being   gradually  imparted  to   the  air 


226  DESCRIPTIVE   CHEMISTRY. 

during  winter,  modifies  the  severity  of  the  cold,  and  ex- 
plains the  fact  that  island  winters  are  less  severe  than 
those  of  continents  or  inland  places. 

The  very  stability  of  Nature  seems  to  depend  upon  this 
quality  of  the  earth's  aqueous  element.  If  the  watery 
masses  of  the  globe,  and  that  large  proportion  of  it  con- 
tained in  our  own  bodies,  lost  and  acquired  heat  as  promptly 
as  mercury,  the  variations  in  temperature  would  be  incon- 
ceivably more  rapid  than  now ;  the  inconstant  seas  would 
freeze  and  thaw  with  the  greatest  facility,  while  the  slight- 
est changes  of  weather  would  send  their  fatal  undulations 
through  all  living  systems.  But  now  the  large  amount  of 
heat  accumulated  in  bodies  of  water  during  summer  is 
given  out  at  a  slow  and  measured  rate;  the  climate  is 
tempered,  and  the  transitions  from  heat  to  cold  are  gradual 
and  moderated. 

397.  Its  Solvent  Power. — Water  possesses  the  power 
of  dissolving  many  solid,  liquid,  and  gaseous  substances. 
This  solvent  power  is  variable  for  different  substances,  and 
at  different  temperatures.  Thus,  a  pound  of  cold  water 
will  dissolve  two  pounds  of  sugar,  while  it  will  only  take 
up  two  ounces  of  common  salt,  two  and  a  half  of  alum,  or 
eight  grains  of  lime.  Heat  generally  increases  the  solvent 
power  of  water;  thus  boiling  water  will  dissolve  17  times 
as  much  saltpetre  as  ice-water.  But  there  are  exceptions 
to  this  rule;  ice-water  dissolves  twice  as  much  lime  as 
boiling  water. 

Water  dissolves  gases  in  the  most  diverse  proportion, 
taking  up  700  times  its  bulk  of  ammonia ;  its  own  bulk  of 
carbonic  dioxide ;  ^  its  bulk  of  oxygen,  and  still  less  of 
nitrogen.  There  is,  therefore,  an  atmosphere  diffused 
throughout  all  natural  waters,  which  is  richer  in  oxygen 
than  common  air,  and  hence  better  adapted  for  supporting 
the  life  of  aquatic  animals.  The  gases  absorbed  by  water 
give  it  a  brisk,  agreeable  flavor,  and,  if  driven  off  by  boil- 
ing, the  liquid  becomes  insipid. 


OXYGEN  AND   ITS  COMPOUNDS.  227 

398.  Purification  of  Water.— Water,  as  found  in  Nature, 
is  never  perfectly  pure,  but  always  contains  variable  quan- 
tities of  mineral  and  organic  substances  which  are"  either 
held  in  suspension  mechanically,  or  are  dissolved  in  it.     It 
is  also  inhabited  by  myriads  of  minute  living  organisms 
known  as  infusoria. 

During  freezing,  the  substances  dissolved  in  water  are 
expelled ;  hence  the  ice  of  sea-water  (as  is  well  known  to 
sailors),  when  melted,  becomes  fresh  water.  For  the  same 
reason,  water  from  melted  ice  contains  neither  air  nor  gas 
— fish  cannot  live  in  it. 

399.  The  best  method  of  purifying  water  is  by  distilla- 
tion (111) ;  to  render  it  perfectly  pure,  it  must  be  redis- 
tilled at  a  low  temperature,  in  silver  vessels.     By  filtration 
through   sand,  crushed  charcoal,  or  other  closely  porous 
media,  water  may  be  deprived  cf  suspended  impurities, 
and  of  all  living  beings.      Boiling  kills  all  animals  and 
vegetables,  expels  gases,  and  precipitates  calcic  carbonate, 
which  constitutes  the  fur  or  crust,  often  seen  lining  tea- 
kettles and  boilers.     Alum   (two  or  three  grains  to   the 
quart)  is  often  used  to  cleanse  muddy  or  turbid  water,  but 
it  does  not   purify  it,  being   merely  decomposed   by  the 
calcic  carbonate  contained  in  the  water,  while  the  alumina 
set  free  carries  down  the  impurities  mechanically ;  but  the 
sulphuric  acid  of  the  alum,  combining  with  the  lime,  forms 
calcic  sulphate,  and  renders  the  water  harder  than  before. 
The  alkalies,  potash,  or  soda,  soften  water  by  decomposing 
and  precipitating   the  earthy  salts ;    but  in  their  turn  re- 
main themselves  in  solution. 

400.  Chemical  Properties. — Although  water  is  neither 
acid  nor  alkaline  in  its  action  on  vegetable  colors,  it  is 
chemically  an  exceedingly  active  body,  inducing  and  under- 
going decomposition,  wrhen  brought  in  contact  with  a  great 
number  of  different  substances.     When  one  atom  of  hydro- 
gon  in  the  water-molecule  is  replaced  by  an  atom  of  a  posi- 
tive radicle,  it  gives  rise  to  a  hydrate ;  when  by  a  negative 


228  DESCRIPTIVE   CHEMISTRY. 

radicle,  to  an  acid  (hydric  salt).  Water  combines  directly 
with  many  substances,  especially  those  which  are  crystal- 
lizable  from  aqueous  solutions.  Thus  held  in  combination, 
it  is  termed  water  of  crystallization.  From  this,  it  appears 
that  the  radicle  oxygen  contained  in  water  is  capable  of 
performing  a  tetradic  linking  function,  which  view  may 
be  graphically  expressed  by  assigning  to  it  the  formula 
H-O-H,  instead  of  H-O-H. 

IV 

401.  Hydric  Dioxide  (H2O2)  is  a  transparent,  colorless, 
syrupy  liquid,  of   1.452   specific  gravity,  which  does  not 
solidify  at  —30°  C.,  and  may  be  evaporated  at  low  tem- 
peratures  in    a  vacuum.      It   has    an   astringent   taste,  a 
decided   odor,  and  possesses  active  bleaching   properties. 
It  is  a  very  unstable  compound,  decomposing    slowly  at 
15°  C.,  while  higher  temperatures,  or  the  contact  of  various 
substances,  causes  it  to  separate  into  water  and  oxygen 
with   explosive    violence.      It   may    be   regarded    as   free 
hydroxyl  (HO),  composed   of  two  atoms  of  a  compound 
monad  radical. 

§  2.   The  Atmosphere. 

402.  Its  Composition. — It  was  not  until  the  year  1774 
that  Lavoisier  pointed  out  the  true  composition   of  the 
atmosphere.     Up  to  this  time  it  was  spoken  of  as  one  of 
the  four  elements  ;  but  the  careful  observations  of  Priestley 
and  Scheele,  and  their  discovery  of  oxygen  gas,  prepared 
the  way  for  a  knowledge  of  its  exact  composition.     It  is 
now  regarded  as  a  mixture  of  several  gases,  nitrogen  and 
oxygen  constituting  its   bulk — the  one   incapable  of  sup- 
porting combustion  or  respiration,  and  the  other  essential 
to  life. 

Air  contains,  Composition  by  Volume.      Composition  by  Weight. 

Oxygen,  20.96  23.185 

Nitrogen,  79.04  76.815 

100.00  100.000 


THE   ATMOSPHERE.  229 

That  the  air  is  made  up  of  these  gases  may  be  ascertained 
both  by  analysis  and  synthesis.  That  it  is  a  mixture  and 
not  a  chetnical  compound  is  made  manifest  by  the  facts 
that  its  components  are  not  united  in  the  ratio  of  their 
atomic  weights,  and  that  each  gas  dissolves  in  water,  inde- 
pendently of  the  other ;  but  the  analyses  of  air  collected 
from  different  parts  of  the  earth,  and  at  different  heights, 
show  a  remarkable  uniformity  in  its  composition.  In  addi- 
tion to  the  oxygen  and  nitrogen  present  in  the  atmosphere, 
there  is  always  a  small  proportion  of  aqueous  vopor,  car- 
bonic dioxide,  and  ammonia. 

403.  The  proportion  of  watery  vapor  in  the  atmosphere 
varies  with  the  temperature.     It  usually  ranges  from  the 
fa  to  the  ^-J-Q  of  the  bulk  of  the  air.     By  passing  known 
quantities  of  air  through  carefully-weighed  tubes  of  po- 
tassic  hydrate,  the  carbonic  dioxide  is  absorbed,  and  its 
proportion   determined.     It   varies  from  3   to   6   paits  in 
10,000  of  air,  and  averages  about  one  volume  in   2,500. 
The  quantity  is  variable  within  the  limits  above    stated. 
It  increases  as  we  rise  from  the  earth,  and  is  less  after  a 
rain,   which   washes   it  down    from   the    air;    it  increases 
during  the  night,  and  diminishes  after  sunrise,  is  less  over 
large  bodies  of  water  than  over  large  tracts  of  land,  and  is 
more  abundant  in  the  air  of  towns  than  in  that  of  the 
country. 

404.  The  Carbonic  Acid  which  is   poured  into  the  at- 
mosphere in  prodigious  quantities  and  from  innumerable 
sources,  is  as  necessary  to  the  vegetable  wrorld,  as  is  oxy- 
gen to   the  animal  world.     It  is  absorbed  by  the  leaves, 
and  minute  as  is  its  proportion,  if  it  were  withdrawn,  the 
vegetable  world  would  quickly  perish.     Liebig  has  shown 
that  the  air  contains  minute  traces  of  ammonia,  which  are 
washed  down,  and  may  be  detected  in  rain-water.     Traces 
of  nitric  acid  have  also  been  frequently  detected.     This 
substance  is  thought  to  be   formed   by  electricity,  every 
flash  of  lighting  which  darts  across  the  sky  combining  a. 


230  DESCRIPTIVE   CHEMISTRY. 

portion  of  the  oxygen  and  nitrogen  along  the  line  of  its 
course,  and  forming  this  acid.  The  saline  particles  of  the 
ocean-waves,  as  they  are  dashed  into  foam  and-  spray,  are 
carried  by  the  winds  far  inland.  All  these  substances  are 
brought  down  by  the  rains,  and  help  to  quicken  the  growth 
of  vegetation. 

405.  Resulting  Properties.— Each   of  the   constituents 
of  the    air  is   essential  to    the   present   order  of  things. 
Oxygen  is  preeminently  its  active  element.     To  duly  re- 
strain this  activity,  the  oxygen  is  diluted  and  weakened 
by  four  times  its  bulk  of  the  negative  element,  nitrogen. 
Their  properties  are  thus  perfectly  adjusted  to  the  require- 
ments of  the  living  world.     Were  the  atmosphere  wholly 
composed  of  nitrogen,  life  could  never  have  been  possible ; 
were  it  to  consist  wholly  of  oxygen,  other  conditions  re- 
maining as  they   are,  the  world   would   run   through  its 
career   with    fearful   rapidity ;    combustion    once   excited, 
would  proceed  with  ungovernable  violence ;  animals  would 
live  with  hundred-fold  intensity,  and  perish  in  a  few  hours. 

406.  The  Atmosphere  and  the  Living  World.— The  re- 
lations of  the  atmosphere  to  living  beings,  the  stability  of 
its  composition,  and  the  wonderful  forces  that  are  displayed 
within  it,  are  full  of  surpassing  interest.     The  vegetable 
world  is  derived  from  the  air ;    it  consists  of  condensed 
gases  that  have  been  reduced  from  the  atmosphere  to  the 
solid  form  by  solar  agency.     On  the  other  hand,  animals, 
which  derive  all  the  material  of  their  structure  from  plants, 
destroy  these  substances  while  living,  by  respiration,  and 
when  dead,  by  putrefaction,  thus  returning  them  again  in 
the  gaseous  form  to  the  air  whence  they  came. 


SULPHUR    AND    ITS    COMPOUNDS.  231 

CHAPTER    XVII. 

THE   SULPHUR   GKOUP. SULPHUR,    SELENIUM,   TELLURIUM. 

§  1.  Sulphur  and  its  Compounds. 

SULPHUR. — Symbol,  S.    Atomic  Weight,  32 ;  Quantivalence,  II.,  IV.,  VI. ; 
Molecular  Weight,  64 ;  Molecular  Volume,  2 ;  Specific  Gravity,  2.05. 

407.  Modifications  of  Sulphur. — Sulphur,  like   oxygen, 
is  capable  of  existing  in  several  different   modifications. 
At  ordinary  temperatures  it  is  solid,  or  nearly  so.     At 
115°  C.,  it  melts  to  a  pale-yellow  liquid.     As  the  tempera- 
ture rises  this  liquid  becomes  viscid,  until,  between  200° 
and  250°  C.,  it  is  too  thick  to  flow.     At  a  still  higher 
temperature  it  again   becomes  fluid,  and  finally  boils  at 
440°  C.     The  density  of  the  vapor  then  diminishes  grad- 
ually, until,  at  1000°  C.,  a  point  is   reached  where  it  is 
32  times  as  great  as  that  of  hydrogen  at  the  same  tem- 
perature.     Sulphur  in   all  its  forms  is  insoluble  in  water 
and  alcohol,  a  poor  conductor  of  heat,  and  a  non-conductor 
of  electricity.     When  heated  in  the  air  to  260°  C.,  it  takes 
fire,  burning  with  a  pale-blue  flame.     The  vapor  of  sulphur 
supports  combustion,   many  metals  taking  fire  in  it,  and 
burning  actively.    When  combined  with  metals  or  positive 
radicals,  sulphur  is  a  dyad,  but  in  other  combinations  it 
may  be  either  a  tetrad  or  hexad. 

408.  Ordinary  Modification  (Sa) — In  this  form,  sulphur 
is  one  of  the  oldest  known  substances,  being  mentioned  in 
the  Bible,  and  in  the  writings  of  the  ancients.     It  exists 
abundantly  in  Nature ;  is  found  in  various  volcanic  regions, 
as  in  the  island   of  Sicily,  where  it  is  mined  in  immense 
quantities  for  the  market.    It  is  deposited  by  many  springs 
and  small  lakes,  being  produced  by  the  decomposition  of 
hydric    sulphide.     The  sulphur  of    commerce  is  prepared 
from  the  impure  native  material,  by  subjecting  it  to  a  rough 
distillation  in  earthen  retorts  which  separates  it  from  min 


232  DESCRIPTIVE   CHEMISTRY. 

eral  impurities.  It  is  also  obtained  from  a  native  ferric  sul- 
phide. This  is  generally  done  by  piling  the  ferric  sulphide 
with  wood,  in  large  heaps  in  the  open  air,  and  setting  these 
on  fire.  A  portion  of  the  ferric  sulphide  burns,  and,  through 
the  heat  attending  its  combustion,  the  remainder  is  also 
decomposed  with  the  liberation  of  sulphur,  which  volatalizes 
and  collects  in  the  fluid  state,  in  basin-shaped  cavities  on 
the  surface  of  the  heap.  In  commerce,  sulphur  exists  in 
forms  due  to  the  different  modes  of  its  preparation :  first, 
as  roll-sulphur  or  brimstone,  obtained  by  running  melted 
sulphur  into  moulds;  second,  as  flour  of  sulphur,  a  pale 
yellow  gritty  powder,  obtained  by  sublimation ;  and,  third, 
as  milk  of  sulphur,  produced  by  the  decomposition  of  solu- 
tions of  certain  sodic  and  potassic  sulphides  with  acids. 
409.  Properties. — In  its  ordinary  modification  sulphur 
F,G.  i6i  is  a  brittle,  yellow  solid,  crystallizing 

in  transparent  right  rhombic  octohe- 
dra,  or  allied  forms  (Fig.  161).  It  is 
soluble  in  carbonic  disulphide,  and  the 
crystals  may  be  obtained  from  this 
solution  by  evaporation. 

410.  Oblique  Prismatic  Sulphur 
Sulphur-Crystals.  (S^).— This  modification  may  be  ob- 
tained by  melting  ordinary  sulphur  in  a  crucible,  allowing  it 
to  cool  until  a  crust  is  formed,  then  breaking  the  crust  and 
pouring  out  the  still  fluid  portion.  The  walls  of  the  crucible 
will  then  be  found  lined  with  a  mass  of  transparent  yellow- 
ish-brown, needle-shaped  crystals  (Fig.  162).  They  are  ob- 
lique rhombic  prisms,  or  modifications  of  Pio  162 
these,  have  a  specific  gravity  of  1.98,  and 
in  the  course  of  a  few  days  pass  sponta- 
neously into  the  ordinary  octahedral  modi- 
fication. They  are  readily  soluble  in  car- 
bonic disulphide. 

411,  Plastic  Sulphur  (Sy).  —  This  va- 
riety is  produced  by  heating  melted  sul-       Crystals  by  Fusion. 


SULPHUR  AND  ITS  COMPOUNDS. 


233 


FIG.  163. 


phur  to  a  temperature  of  from  260°  to  300°  C.,  and  then  sud- 
denly cooling  it  by  pouring  it  in  a  thin  stream  into  water 
(Fig.  163).  It  is  a  dark-brown  tenacious  mass,  which  may  be 
drawn  into  threads  like  In- 
dia-rubber. It  has  a  specific 
gravity  of  1.95,  and  is  inso- 
luble in  carbonic  disulphide. 
It  gradually  changes  to  the 
ordinary  modification.  Sul- 
phur is  consumed  largely  in 
the  manufacture  of  hydric 
sulphate,  of  gunpowder,  and 
of  friction-matches.  Milk  of 
sulphur  is  extensively  used 
in  medicine.  The  plastic 
modification  is  often  em- 
ployed to  take  impressions 
of  medals,  coins,  and  simi- 
lar objects. 

412.  Hydric  Sulphide  (H2S)  (Sulphuretted  Hydrogen). 
— Hydric   sulphide    was   discovered  by  Scheele,  in  1777. 
It  is  found  abundantly  in  Nature  as  a  volcanic  product, 
as  the  essential  ingredient  to  which  the  waters  of  so-called 
sulphur-springs  owe  their  flavor,  and  as  one  of  the  bodies 
resulting  from  the  decay  of  organic  matter. 

413.  Preparation  and  Properties. — It  is  usually  obtained 
by  the  action  of  dilute  hydric  sulphate  on  ferrous  monosul- 
phide. 

Fe'S  +  HaS04  =  Fe"SO4  +  H2S 

Fig.  164  represents  a  convenient  arrangement  for  its  evo- 
lution. The  ferric  monosulphide  should  be  broken  into 
small  lumps  and  placed  in  the  flask.  The  cork  and  tubes 
may  then  be  adjusted,  and,  first,  water,  and  then  hydric 
sulphate  poured  in  through  the  funnel-tube.  The  gas  is 
absorbed  by  the  water  of  the  second  vessel.  The  solution 
must  be  kept  in  tightly-secured  bottles,  as,  if  exposed 


Amorphous  Sulphur. 


234 


DESCRIPTIVE   CHEMISTRY. 


FIG.  164. 


to  the  air,  it  is  gradually  decomposed.  Hydric  sulphide 
is  a  colorless  transparent  gas,  having  the  well-known  odor 
of  rotten  eggs.  Cooled  to  74°,  or  submitted  to  a  pressure 
of  17  atmospheres  at  10°,  it  con- 
denses to  a  colorless  mobile  liquid 
of  0.9  specific  gravity,  which  freez- 
es at  —85°,  the  frozen  portion  sink- 
ing in  the  liquid.  It  readily  dis- 
solves in  water,  imparting  to  the 
solution  its  taste  and  smell.  Its 
reaction  on  vegetable  colors  is 
slightly  acid,  and  heated  in  the  air 
it  burns  with  a  pale-blue  flame. 
When  breathed  it  is  highly  poi- 
sonous, and  even  when  much  di- 
luted with  air  it  has  proved  fatal  to  many  of  the  lower 
animals.  Hydric  sulphide  is  used  extensively  in  chemical 
operations  as  a  re-agent.  Its  action  upon  solutions  of  the 
metals  may  be  shown  by  the  apparatus  represented  in  the 

FIG.  165. 


Liberation  of  Hydric  Sulphide. 


Precipitation  of  Metals  by  Hydric  Sulphide. 

accompanying  cut  (Fig.  165).     The  gas  is   evolved  from 
ferrous  sulphide  in  a  two-necked  bottle,  and  passed  through 


SULPHUR  AND   ITS   COMPOUNDS.  235 

a  second  bottle  containing  a  little  water,  after  which  it  suc- 
cessively passes  through  bottles  containing  solutions  of 
cupric  sulphate,  zinc  sulphate,  ferrous  sulphate,  and  lead 
sulphate.  The  cupric  sulphate  in  the  first  bottle  will  give 
a  black  precipitate,  that  in  the  second  a  white,  while  the 
last  ones  yield  black  precipitates. 

414.  Chloric  Bisulphide,  C12S2. — This  compound,  more 
generally  termed  chloride  of  sulphur,  is  obtained  by  passing 
dry  chloric  gas  over  melted  sulphur.     It  is  a  deep  orange- 
yellow   liquid    of  peculiar   disagreeable   odor,   boiling   at 
136°  C.     It  is  instantly  decomposed   by   water.     Chloric 
disulphide  is  employed  in  the  vulcanization  of  caoutchouc. 

415.  Sulphur  and  Oxygen. — Sulphur   may  unite  with 
oxygen  as  a  dyad,  tetrad,  or  hexad.     The  following  are  the 
oxides  and  acids  with  which  we  are  acquainted : 

Sulphurous  oxide,  SIVO2.  Sulphurous  acid,  HaSIVOj. 

Sulphuric        "      SVI0S.          Sulphuric        u    H3SVIO4. 

416.  Sulphurous  Oxide,   SO2.— This   substance  occurs 
among  the    products    of  volcanic   action,    and    is    always 
formed  by  the  combustion  of  sulphur  in  air,  or  in  pure 
oxygen, th  us : 

S,  +  0.=2(S03) 

It  is  a  transparent,  colorless  gas,  of  2.25  specific  gravity, 
having  a  pungent,  suffocating  odor,  familiarly  known  in  the 
case  of  a  burning  match.  It  extinguishes  combustion; 
hence  sulphur  is  often  thrown  into  the  fire  to  quench  the 
burning  soot  of  chimneys.  It  has  a  strong  attraction  for 
water.  Allowed  to  escape  into  the  air,  it  forms  white  fumes 
with  its  moisture,  and  a  piece  of  ice  thrust  into  the  gas  is 
instantly  liquefied.  Water  at  60°  F.  takes  up  large  quan- 
tities of  this  acid,  the  solution  formed  having  the  taste  and 
smell  of  the  gas.  By  cold  or  pressure  it  condenses  into  a 
liquid,  of  1.49  specific  gravity,  which  evaporates  so  fast 
that  the  cold  generated  will  freeze  water  even  in  a  red-hot 
crucible.  At  —76°  C.  it  becomes  solid. 


236 


DESCRIPTIVE  CHEMISTRY. 


FIG.  166. 


Bleaching  by  Sulphurous  Oxide. 


417.  Uses. — Sulphurous  oxide  is  used  as  a  disinfectant, 
and  in  bleaching  woolen  and  straw  fabrics.    The  goods  are 

moistened,  and  suspended  in 
large  chambers,  or,  in  a  small 
way,  they  are  put  into  inverted 
barrels,  and  exposed  to  the 
fumes  of  burning  sulphur.  The 
effect  is  produced,  not  by  de- 
stroying the  coloring  matter,  as 
in  the  case  of  chlorine,  but  by 
the  union  of  the  acid  with  the 
coloring  matter,  which  forms  a 
white  compound.  If  a  red  rose 
is  held  over  burning  sulphur, 
it  is  whitened,  but  the  color  is 
at  once  restored  by  weak  sul- 
phuric acid,  which,  being  stronger,  discharges  sulphurous 
oxide  from  combination.  The  bleaching  power  of  sul- 
phurous oxide  upon  flowers  may  be  illustrated  by  burning 
sulphur  under  a  glass,  within  which  are  some  highly- 
colored  flowers.  (Fig.  166.)  If  woolens,  after  sulphur- 
bleaching,  are  washed  with  a  strong  alkaline  soap,  the  acid 
is  neutralized  by  the  alkali,  the  coloring  matter  liberated, 
and  the  yellowish  color  restored. 

418.  Sulphurous   Acid,  Hydric  Sulphite,  H2SO3.— The 
solution  of  sulphurous  oxide  in  water  contains  a  definite 
compound  of  the  form  H2SO3,  which  is  possessed  of  strong 
acid  properties.    It  is  sometimes  used  for  the  same  purposes 
for  which  sulphurous  oxide  is  employed.     The  hydrogen 
in  this  compound  is  replaceable  wholly  or  in  part  by  me- 
tallic elements,  giving  rise  to  numerous  salts  known  col- 
lectively as  sulphites. 

419.  Sulphuric  Oxide,  SO3. — This  may  be  obtained  in 
the  form  of  a  white  snowy  solid,  by  heating  disulphuric 
acid,  and  collecting   the  fumes  which    pass   over   into  a 
receiver  surrounded  by  a  freezing  mixture.     While  in  this 


SULPHUR  AND  ITS  COMPOUNDS. 


237 


condition,  it  exhibits  no  acid  properties,  and  may  be  handled 
with  impunity,  if  the  hands  are  dry.  But  it  fumes  in  the 
air,  and  rapidly  absorbs  moisture.  When  thrown  into 
water  it  hisses  like  a  hot  iron,  and  the  solution  thus  formed 
possesses  all  the  properties  of  the  ordinary  acid. 

420.  Sulphuric  Acid,  Hydric  Sulphate,  H2SO4.— This 
important  chemical  compound  was  known  as  early  as  the 
fifteenth  century.  It  is  found  native  in  a  dilute  condition, 
in  volcanic  regions,  and  in  the  waters  of  some  springs  and 
rivers.  Sulphuric  acid  may  be  prepared  on  a  small  scale 

FIG.  167. 


FIG.  16$. 


Preparation  of  Sulphuric  Acid. 

in  an  apparatus  represented  by  Fig.  167.  A  large  glass 
balloon,  #,  is  connected  by  tubes  with  three  flasks.  Flask 
b  supplies  it  with  sulphurous  oxide;  c,  with  nitric  dioxide; 
d,  with  steam,  and  the  short  tube  furnishes  air.  These 
four  substances  re- 
act upon  each  other 
with  the  continued 
production  of  sul- 
phuric acid.  In 

the  manufactory  the    '  Liberate  sulphuric  Acid. 

balloon  is  represent- 
ed by  large  chambers  lined  with  sheet-lead,  and  the  flasks 
by  furnaces  (Fig.  168).     In  one  furnace  sulphur  is  heated, 


238  DESCRIPTIVE   CHEMISTRY. 

and  pours  into  the  chamber  sulphurous  oxide,  SO,.  In 
another  nitre  is  heated  in  an  iron  pot  with  sulphuric  acid, 
by  which  fumes  of  nitric  acid,  HNO3,  are  produced  and 
delivered  into  the  chamber.  The  HNO3  is  quickly  deprived 
of  an  atom  of  oxygen  by  the  sulphur,  yielding  water  and 
nitrogen  tetroxide,  NCO4,  Steam  and  air  are  thrown  into 
the  chamber  by  another  flue,  and  thus  the  conditions  of 
action  are  secured. 

421.  The  process  depends  upon  the  property  possessed 
by  the  higher  oxides  of  nitrogen  of  oxidizing  sulphurous 
oxide,  at  the  expense  of  the  oxygen  of  the  atmosphere. 
The  sulphurous  oxide  is  converted  into  the  sulphuric,  the 
oxygen  being  derived  from  the  air,  and  the  nitric  dioxide 
being  the  carrier  that  transports  it.  A  small  quantity  of 
NaO2  may  thus  form  an  endless  quantity  of  SO3,  which 
unites  with  the  water  present  to  form  sulphuric  acid,  H2SO4. 
These  changes  are  represented  in  the  following  scheme : 


FROM   AIR,       O 
FBOM   THE 

FURNACE,  N202  — -  N204  — ^  N202 *  N204  ^  N208 

AS  STEAM,   H2O  v  \  H20, 

FROM  THE  ^V  \ 

FURNACE,   S  Oj^^X^     \  8  Oa 

~  H2S04 


The  large  chambers  of  the  manufactory  are  divided  by 
leaden  partitions  with  narrow  openings,  which  serve  to 
facilitate  the  intermixture  of  the  gases  as  they  pass  on 
through  the  apartments.  The  bottom  of  the  chamber  is 
always  kept  covered  with  water  to  the  depth  of  two  or  three 
inches,  to  absorb  the  acid  as  it  falls.  When  the  water  has 
acquired  a  density  of  1.5,  by  the  absorption  of  acid,  it  is 
drawn  off  and  boiled  down  in  glass  or  platinum  retorts, 
until  it  has  a  specific  gravity  of  about  1.8.  The  acid  thus 
obtained  has  the  formula  H2SO4,  and  constitutes  the  or- 
dinary sulphuric  acid  of  commerce. 


SULPHUR  AND  ITS  COMPOUNDS.  239 

422.  Properties. — Sulphuric  acid  is  a  thick,  oily  liquid 
of  1.85  specific  gravity,  without  odor,  and  has  at  first  a 
soapy  feel,  but  it  speedily  corrodes  the  skin,  causing  an 
intense  burning  sensation.     It  is  the  most  powerful  of  acids, 
and  has  an  intense  affinity  for  water.     When  a  splinter  of 
wood  is  dipped  into  it  for  a  short  time,  it  turns  black,  the 
acid  taking  away  from  it  the  elements  of  water,  and  leaving 
the  carbon.     In  like  manner,  it  decomposes  and  chars  the 
skin  and  most  other  organic  substances  by  removing  their 
water.     If  a  little  concentrated  acid  is  exposed  to  the  open 
air  in  a  shallow  dish  it  will  soon  double  its  weight 

from  the  moisture  absorbed.  When  sulphuric  acid  FlG- 
and  water  are  mixed  they  shrink  in  bulk,  and  heat 
is  produced.  A  mixture  of  four  parts  concentrated 
acid  to  one  part  water  (Fig.  169)  evolves  sufficient 
heat  to  boil  the  ether  in  a  test-tube.  The  concen- 
trated acid  freezes  at  about  —  30°  F.,  and  boils  at 
640°  F.  Pure  sulphuric  acid  is  colorless,  but  slight 
traces  of  organic  matter,  as  dust  or  straws,  turn  it  of  the 
dark  shade  usually  seen  in  commerce.  The  commercial 
acid  is  cheap,  but  impure,  containing  traces  of  lead,  arsenic, 
potash,  hydric  chloride,  and  sulphurous  oxide.  The  test 
for  sulphuric  acid  is  a  solution  of  baric  chloride  (440). 

423.  Uses. — Sulphuric  acid  is  the  most  important  sub- 
stance used  in  manufactures.      It  is  employed  to  make 
sodic  and  chloric  carbonate,  citric,  tartaric,  acetic,  and  nitric 
acids,  sodic  and   magnesic  sulphate,  and  various   paints; 
also,  in  dj  eing,  calico-printing,  gold  and   silver  refining, 
and  in  purifying  oil  and  tallow.     Its  chemical  uses  are  in- 
numerable.    Disulphuric  acid,  HSSSO7,  is  also  known  as 
Nordhausen  sulphuric  acid,  or  fuming  sulphuric  acid,  and 
is  manufactured  by  the  original  process — the  distillation  of 
dried  ferrous  sulphate  in  earthen  retorts.  It  is  a  heavy,  oily 
liquid,  of  1.9   specific  gravity,  fuming  strongly  in  contact 
with  the  air.     Heat  decomposes  it  into  sulphuric  acid  and 
sulphuric   oxide.     The   method  by  which   this  acid  is  ob- 

11 


240  DESCRIPTIVE  CHEMISTRY. 

tained  from  ferrous  sulphate,  or  "  green  vitriol,"  has  given 
rise  to  the  name  of  "oil  of  vitriol,"  by  which  sulphuric  acid 
is  generally  known. 

§  2.  Selenium  and  Tellurium. 

424.  History. — Selenium  and  Tellurium  are  elements 
closely  allied  to  sulphur.  They  form  compounds  with  dry 
hydrogen,  H2Se,  and  H2Te,  similar  to  H2S ;  and  also  com- 
pounds with  oxygen  and  hydrogen,  resembling  sulphurous 
and  sulphuric  acids.  Selenium  is  a  rare  substance,  existing 
in  several  modifications,  apparently  analogous  to  those  of 
sulphur.  Its  name  is  derived  from  a  Greek  word,  meaning 
the  moon.  At  ordinary  temperatures  it  is  a  solid  of  a 
brownish-red  color,  and  with  a  lustre  somewhat  resembling 
that  of  the  metals.  Selenium  boils  at  700°  C.  Heated  in 
the  air  it  burns,  emitting  an  intolerable  odor  resembling 
decayed  horse-radish.  Tellurium  was  first  distinguished  in 
1798,  by  Klaproth,  who  named  it  tellurium,  from  the  Latin 
"  tellus,"  the  earth.  It  is  found  in  Nature,  but  is  exceed- 
ingly rare.  It  is  a  tin-white  brittle  metal,  crystallizing  in 
rhombohedrons,  melting  at  about  500°  C.,  and  volatilizing 
at  a  white  heat.  Heated  in  the  air  it  takes  fire,  and  burns 
with  a  lively  blue  flame,  edged  with  green.  The  vapor  of 
tellurium  has  a  greenish-yellow  color. 


COPPER  AND  ITS   COMPOUNDS.  241 

CHAPTER   XVIIL 

COPPER  AND    MERCURY. 

§  1.    Copper  and  its  Compounds. 

COPPEB. — Symbol,  Cu.    Atomic  Weight,  63.5 ;  Quantivalence,  II. ;  Specific 
Gravity,  8.9. 

425.  Copper. — This  metal,   well  known   since  earliest 
times,  is  often  found  native  in  masses  of  considerable  mag- 
nitude.    It  is  obtained  on  a  large  scale  by  the  decomposi- 
tion of  ores,  of  which  copper  pyrites   (Cu2Fe2S4),  cuprous 
oxide  (Cu2O),  and  malachite   (Cu2H2CO5),  are  among  the 
most  important.     The  processes  of  its  extraction  are  very 
complicated.    Metallic  copper  is  tough,  malleable,  and  of  a 
red  color.     The  metal  may  be  stiffened  by  hammering,  and 
softened  by  heating  and  suddenly  cooling  in  water ;  the  re- 
verse of  the  effect  produced  upon  steel.     In  dry  air  it  is 
hardly  acted  upon,  but  in  a  damp  atmosphere  it  acquires 
a  green  crust  of  a  cupric  carbonate  familiarly  known  as  ver- 
digris.    Copper  is  an  excellent  conductor  of  heat  and  elec- 
tricity, and  is  extensively  used  for  telegraph-wires.    Being 
little  affected  by  the  air,  it  is  better  adapted  for  culinary  uten- 
sils than  iron.     Vegetable  acids,  however,  dissolve  it  in  the 
cold  state ;  hence  sauces  containing  vinegar,  and  preserved 
fruits  or  jellies,  should  not  be  allowed  to  remain  in  copper 
vessels,  as  the  salts  produced  are  poisonous.    Copper  forms 
alloys  with  other  metals,  among  which  may  be  mentioned 
brass,  German-silver,  bronze  and  speculum  metal. 

426.  Cupric  Oxide,  CuO.— This  oxide  is  found  native 
as  the  mineral  melaconite.     It  may  be  artificially  prepared 
by  strongly  heating  cupric  nitrate  (CuN2O6  +  3H2O).     It  is 
a  black  or  brownish-black  powder,  fusible  at  red-heat.     It 
is  used  in  organic  analysis  as  a  source  of  oxygen,  and  in 
the  manufacture  of  glass  and  porcelain  to  impart  a  green 


DESCRIPTIVE  CHEMISTRY. 

color.  Cupric  sulphate  (Blue  Vitriol),  (CuS04+  5H2O), 
is  obtained  by  heating  cupric  sulphide  in  contact  with  air, 
or  by  the  action  of  sulphuric  acid  on  metallic  copper. 
It  is  used  largely  in  dyeing  and  calico-printing,  and  as 
a  source  of  many  of  the  pigments  containing  copper. 
Cupric  arsenite,  or  Scheele's  green,  is  obtained  by  mixing 
solutions  of  cupric  sulphate  with  sodic  arsenite.  It  is  of 
bright-green  color,  exceedingly  poisonous,  and  is  used  as 
a  pigment.  In  commerce  it  is  called  Paris  green. 

§  2.  Mercury  and  its  Compounds. 

MERCURY. — Symbol,  Hg.  (Hydrargyrum).     Atomic  Weight,  200 ;   Quan- 

tivalence,  II.;  Molecular  Weight,  200 ;  Molecular  Volume,  2 ; 

Specific  Gravity,  13.59. 

427.  History. — This  remarkable  element  is  often  found 
native  in  little  globules,  disseminated  through  certain 
ores,  particularly  cinnabar,  or  mercuric  sulphide  (HgS). 
It  is  obtained  on  a  large  scale  by  distillation  of  the  cin- 
nabar-ore, either  alone  or  mixed  with  burnt  lime  or  forge- 
scales.  Mercury  has  a  silver-white  color,  and  a  brilliant 
lustre,  and  is  remarkable  in  being  a  liquid  at  ordinary 
FIG  170  temperatures.  Its  specific  grav- 

ity is  nearly  twice  that  of  iron, 
a  ball  of  which  will  sink  half-way 
into  the  liquid  mercury,  while 
wood  will  float  upon  its  surface 
(Fig.  170). 

It  solidifies  when  cooled  to 
-40°  C.,  and  is  then  soft  and  mal- 

Ball  sinking  in  Liquid.  ^^  ^  .f  ^^  ^  &  ^^ 

lower  temperature  it  becomes  brittle.  It  boils  at  about 
350°  C.,  and  slowly  volatilizes  at  all  temperatures  above 
15°  C.  Metallic  mercury  is  used  extensively  in  the  manu- 
facture of  philosophical  instruments,  thermometers,  barom- 


MERCURY  AND   ITS  COMPOUNDS.  243 

eters,  and  to  form  an  alloy  with  tin  for  coating  the  backs 
of  mirrors.  It  is  also  used  largely  in  the  extraction  of 
gold  and  silver  by  the  process  of  amalgamation.  The 
alloys  of  mercury  are  called  amalgams. 

428.  Mercuric  Oxide,  HgO. — This  substance,  commonly 
known  as  red  oxide  of  mercury,  or  red  precipitate,  may  be 
formed  by  heating  metallic  mercury  up  to  600°  F.,  with 
free  access  of  air.      A  still   higher  heat  decomposes  it, 
liberating  the  oxygen,  and  reducing  the  mercury  to  the 
metallic  state.      This  oxide  furnishes  a  ready  source  of 
oxygen  gas,  being  the  compound  from  which  oxygen  was 
first  obtained  by  Priestley,  and  by  which  Lavoisier  proved 
the  composition  of  air. 

429.  Mercuric  Chloride,  HgCl2  (Corrosive  Sublimate). 
— This  compound  is  prepared  by  mixing  mercuric  sulphate, 
HgSO4,  with  an  equal  weight  of  common  salt,  and  apply- 
ing heat  to  the  mixture.     It  is  soluble  in   water  and  in 
alcohol.     Its  solution  has  a  metallic,  acrid  taste,  and  an 
acid  reaction.     It  is  a  deadly  poison,  and  accidents  have 
occurred  from   its  substitution  for  calomel.      The  proper 
antidote  for  it  is  white  of  egg,  which  forms  with  it  an  in- 
soluble  inert    compound.      This  substance  is   used   in   a 
process  for   preserving   wood,   by  impregnation  with   its 
solution,  which  is  termed  kyanizing. 

430.  Mercurous    Chloride    (Calomel),  Hg8Ci2.  —  This 
compound  is  found  native  as  "  horn  quicksilver"      It  is 
prepared    by  triturating    mercuric    chloride,   HgCl2,  with 
mercury,  or  is  precipitated  whenever  solutions  of  any  mer- 
curous    compounds    and    a    soluble    chloride    are    mixed 
together.     Sublimed  calomel  is  a  crystalline  powder,  white 
or  dirty  white  in  color ;  very  heavy,  tasteless,  and  inodor- 
ous.    Calomel  is  decomposed  by  light.     It  has  been  very 
extensively  used  in  medicine,  and  is  much  less  poisonous 
than  "  corrosive  sublimate." 

431.  Mercuric  Sulphide    (Cinnabar),    HgS,   occurs    in 
large  beds  at  Almaden,  in   Spain,  and  is  also  found   in 


244  DESCRIPTIVE   CHEMISTRY. 

extensive  deposits  in  California.  It  is  produced  in  con- 
siderable quantity  by  artificial  means,  and  sold  as  a  pigment 
under  the  name  of  vermilion. 


CHAPTER   XIX. 

THE   CALCIUM   GROUP — CALCIUM,  STRONTIUM,  BARIUM,  LEAD. 

§  1.    Calcium  and  its  Compounds. 

CALCIUM.— Symbol,  Ca.  Atomic  Weight,  40 ;  Quantivalence,  II.  and  IV. ; 
Specific  Gravity,  1.57. 

432.  History. — Calcium  is  one  of  the  most  abundant 
constituents  of  the  crust  of  the  earth.     It  occurs  in  the 
extensive  layers  of  limestone,  marble,  and  chalk,   as  a  car- 
bonate.    In  gypsum  and  alabaster  it  is  found  as  a  sulphate, 
while  as  a  phosphate  it  forms  an  important  constituent  of 
the   bones  of  animals.     The  metal  itself  is   rare,  and   is 
prepared  by  passing  a  galvanic  current  through  fused  calcic 
chloride.     It  is  a  light-yellow  metal,  somewhat  harder  than 
lead,  very  malleable,  melts  at  a  red  heat,  and  oxidizes  in 
the  air. 

433.  Calcic  Oxide,  CaO  (Lim*).— This  well-known  sub- 
stance do3s  not  occur  in  Nature,  but  is  prepared  by  burning 
calcic  carbonate,  limestone   (CaCO3),  in    large   masses   in 
kilns.    The  carbonic  dioxide  is  driven  off  by  the  heat,  and  a 
white,  stony  substance  remains,  called  quick-lime,  or  caustic 
lims.     One  ton  of  good  limestone  yields  11  cwt.  of  lime. 
When  this  is  exposed  to  the  air  it  first  rapidly  imbibes 
moisture  and  crumbles  to  powder.     This  gradually  absorbs 
carbonic    dioxide,    and,    becoming    less   and    less  caustic, 
regains  the  neutral  condition  of  the  carbonate. 

434.  Calcic  Hydrate. — When   water   is    poured   upon 
quicklime  it  absorbs  it  (every  28  Ibs.  of  lime  taking  nine 


CALCIUM  AND   ITS   COMPOUNDS.  345 

pounds  of  water),  swells  to  thrice  its  original  bulk,  crum- 
bles to  a  fine  white  powder,  and  is  converted  into  calcic 
hydrate,  CaH2O2.  This  process  is  called  slacking,  and 
sufficient  heat  is  often  produced  by  the  chemical  action  to 
ignite  wood.  Lime-water  is  a  saturated,  transparent  solu- 
tion of  calcic  hydrate  in  water.  Cream  or  milk  of  lime  is 
a  thick  mixture  of  the  hydrate  with  water,  such  as  is  used 
in  whitewashing.  In  tanneries  the  hides  are  immersed  in 
milk  of  lime,  which  partially  decomposes  them,  so  that  the 
hair  may  be  easily  removed.  Calcic  hydrate  exhibits  the 
properties  of  a  strong  alkali,  decomposing  organic  tissues 
and  saturating  the  strongest  acids.  It  is  more  soluble  in 
cold  than  in  hot  water.  Hence,  when  cold  saturated  lime- 
water  is  boiled,  a  portion  of  the  hydrate  is  deposited. 
Slacked  lime  is  extensively  used  in  chemical  manufactures, 
and  as  a  fertilizer.  Its  value  as  a  fertilizer  is  due  to  the 
property  which  it  has  of  decomposing  organic  and  inor- 
ganic constituents  of  soil. 

435.  Mortar  and  Cement.  —  Lime,   mixed   with   sand, 
forms  the  mortar  employed  by  builders  to  cement  stones 
and  bricks.     To  make  the  best  mortar,  the  lime  should  be 
perfectly  caustic  and  the   sand   sharp  and  cross-grained. 
The  nature  of  the  changes  by, which   the  mortar   becomes 
hardened  is  not  satisfactorily  explained.     It  is  supposed  to 
be  owing  in  part  to  the  absorption  of  carbonic  dioxide  from 
the  air  by  the  lime,  and  the  subsequent  hardening  into  a 
calcic  carbonate.     In  time  the  lime  also  partially  combines 
with  the  silica  of  the  sand,  forming  an  exceedingly  hard  sili- 
cate of  lime.     Common  mortar,  when  laid  in  water,  not  only 
refuses  to  harden,  but  its  lime  gradually  becomes  dissolved 
out  and  washed  away.      Hydraulic  cement  possesses  the 
property   of   solidifying    under    water.       This    quality   is 
owing  to  the  presence  of  clay  (aluminic  silicate)  in  the  lime 
of  which  it  is  composed. 

436.  Bleaching-Powder.  —  When    chlorine    is    passed 
through  recently-slacked  lime,  large  quantities  of  the  gas 


246  DESCRIPTIVE   CHEMISTRY. 

are  absorbed,  forming  the  bleaching -poivder  of  commerce. 
The  chemical  constitution  of  this  substance  is  yet  a  matter 
of  doubt.  It  is  generally  regarded  as  a  mixture  of  calcic 
hypochlorite  with  calcic  chloride,  but  it  is  not  impos- 
sible that  it  may  correspond  to  the  graphic  expression 
Cl-Ca-O-Cl.  It  is  a  white,  sparingly  soluble  powder, 
used  in  great  quantities  for  bleaching  purposes.  In  the 
bleaching  of  cotton  fabrics,  the  goods  are  first  freed 
from  all  greasy  impurities,  and  then  digested  in  a  solu- 
tion of  this  powder.  They  are  next  dipped  into  very 
dilute  sulphuric  acid,  by  which  chlorine  is  liberated,  and 
exerts  its  bleaching  power.  This  process  requires  to  be 
repeated  several  times  before  the  color  is  entirely  dis- 
charged ;  after  which  the  goods  are  thoroughly  washed  in 
water,  in  order  to  remove  all  trace  of  acid  from  the  fibre 
of  the  cloth. 

437.  Calcic  Sulphate,  CaSO4. — This  salt  occurs  native 
as  the  mineral  anhydrite,  and  is  produced  artificially  on  a 
large  scale  by  calcining  powdered  gypsum  (CaSO4  +  2H2O), 
at  about  250°  C.     Thus  prepared  it  constitutes  "  plaster  of 
Paris,"  and  possesses  the  property  of  combining  with  water 
when  made  into  a  paste.     It  is  used  for  taking  casts  by 
running  the  mixture  into  hollow  moulds,  and  colored  and 
mixed  with  glue,  for  producing  the  ornamental  designs 
known  as  stucco-work.      Calcic  sulphate  dihydrate  (gyp- 
sum, alabaster),  CaSO4  +  2H2O,  occurs  in  many  parts  of 
the  world,  forming   extensive    rocky  beds.     In   its   pure, 
transparent  form,  it  is  known  as  selenite,  and  in  its  com- 
pact and  earthy  varieties  as  gypsum  and  alabaster.     Gyp- 
sum is  used  extensively  as  a  fertilizer. 

438.  Calcic  Carbonate,  CaOO3.— Vast  deposits  of  this 
substance  are  distributed  all  over  the  globe  in  the  form  of 
limestones,  marbles,  chalks,  marls,  coralreefs,  shells,  etc. 
Numerous  and  extensive  as  are  these  deposits,  it  is  con- 
jectured that  they  are  all  of  animal  origin.     The  densest 
limestone  and  the  softest  chalk  are  found  to  consist  of  the 


STRONTIUM  AND   BARIUM.  247 

aggregated  skeletons  or  shells  of  myriads  of  tribes  of  the 
lower  animals,  which  have  existed  in  some  former  period 
of  the  world's  history.  The  formation  of  coral-reefs,  which 
are  sea-islands  of  calcic  carbonate,  built  up  from  the  depths 
of  the  ocean  by  minute  aquatic  animals,  is  an  example  of 
similar  deposits  now  in  process  of  formation.  Calcic  car- 
bonate is  decomposed  by  heat  into  calcic  oxide  and  car- 
bonic dioxide.  Hydro-calcic  carbonate,  CaH2C2O6.  When 
calcic  carbonate  is  acted  upon  by  water  containing  carbonic 
dioxide  in  solution,  it  dissolves  with  the  formation  of  this 
compound.  This  solution,  naturally  formed,  constitutes  one 
of  the  varieties  of  hard  water,  which  is  generally  met  with 
in  limestone  districts. 

439.  Calcic  Phosphate,  Ca3  (PO4)2.— This  is  the  earthy 
constituent  of  the  bones  of  animals.     They  obtain  it  from 
the  plants,   and  the  plants  in  turn  take  it  from   the  soil. 
It  is  found  abundantly  in  the  grains  of  cereals,  which,  as 
the  supply  is  limited  in  the  soil,  rapidly  exhaust  it,  when 
they  are  cultivated,  year  after  year;  hence  the  importance 
of  restoring  to  the  land  the  phosphates  when  they  are  re-r 
moved  by  the  crops. 

§  2.  Strontium  a/id  Barium. 

440.  Strontium — Resembles  calcium,  both   in   appear- 
ance and  properties.     It  is  obtained  from  its  chloride,  and 
is  a  pale-yellow  metal,  of  specific  gravity  2.54.     It  does 
not   change    in   dry  air",  but    decomposes    water   readily, 
evolving  hydrogen.    Barium  is  a  light-yellow  metal,  which 
rapidly  oxidizes  in    the   air,   decomposes  water,  and  has 
a  specific  gravity  of  4.0.    The  compounds  of  these  elements, 
though  less  widely  distributed,  are  allied  to  the  correspond- 
ing compounds  of  calcium.     The  nitrate  of  strontium  is 
used  in  pyrotechny,  and  imparts  to  flame  a  beautiful  crim- 
son color.    Baric  oxide,  or  baryta  (BaO),  is  a  gray  powder 
having  a  strong  attraction  for  water^  which  it  absorbs  on 


248  DESCRIPTIVE   CHEMISTRY. 

exposure  to  the  air,  forming  baric  hydrate.  Baric  chloride 
dihydrate  (BaCl2  +  2H2O)  is  interesting  chiefly  as  the 
usual  test  for  sulphuric  acid,  with  which  it  gives  a  dense, 
white,  insoluble  precipitate  of  baric  sulphate.  It  has  been 
employed  in  medicine.  Baric  sulphate,  or  heavy  spar, 
occurs  in  large  quantities,  and  when  ground  is  extensively 
consumed  under  the  name  of  barytes,  in  the  adulteration 
of  paints. 

§  3.  Lead  and  its  Compounds. 

LEAD. — Symbol,  Pb.  (Plumbum).     Atomic  Weight,  207 ;  Quantivalence, 
II.  and  IV. ;  Specific  Gravity,  11.44. 

441.  Lead. — This  useful  and  common  metal  is  of  doubt- 
ful native  occurrence,  but  is  obtained  from  various  ores,  of 
which  the  mineral  galena,  a  plumbic  sulphide,  is  the  most 
important.  Lead  is  a  soft,  blue  metal,  easily  scratched  by 
the  nail,  and  leaving  a  stain  when  rubbed  upon  paper. 
It  is  highly  malleable,  but  not  very  ductile.  In  the  air  a 
film  of  oxide  rapidly  forms  on  its  surface,  which  protects  it 
from  further  corrosion.  It  melts  at  about  330°  C.,  and  on 
solidifying  contracts  to  such  an  extent  as  to  render  it  unfit 
for  castings.  Lead  is  much  used  in  the  manufacture  of 
pipe  for  conducting  drinking-water  to  the  different  parts 
of  dwellings. 

If  lead  is  exposed  to  the  combined  action  of  pure  water 
and  air,  plumbic  hydrate  is  formed  on  the  exposed  surface, 
which  is  dissolved  by  the  water  with  which  it  is  in  contact. 
This  solution  of  plumbic  hydrate  absorbs  carbonic  dioxide 
with  formation  of  plumbic  carbonate,  a  highly-poisonous 
compound.  The  presence  of  chlorides  or  nitrates  assists 
this  corroding  action,  while  it  is  retarded  by  the  sulphates, 
phosphates,  or  carbonates.  Hydro-calcic  carbonate,  a  salt 
found  in  many  spring-waters,  also  prevents  this  corrosion 
by  depositing  a  coating  on  the  exposed  surface.  As  all 
lead-salts  are  poisonous,  it  is  not  safe  to  use  water  which 


LEAD  AND   ITS   COMPOUNDS.  249 

has  been  kept  in  cisterns  lined  with  lead,  or  which  has 
been  conveyed  through  lead  pipes,  unless  it  has  been  care- 
fully ascertained  that  the  water  contains  such  foreign 
matters  as  will  prevent  its  action  upon  the  metal.  Lead 
in  the  presence  of  air  and  moisture  is  acted  upon  by  feeble 
acids.  Hence  the  use  of  vessels  made  of  lead  should  be 
carefully  avoided  in  the  culinary  department.  This  metal 
is  extensively  used  in  the  arts,  both  alone  and  alloyed  with 
other  metals.  An  alloy  prepared  by  mixing  2  parts  of 
arsenic  with  100  parts  of  lead  is  employed  in  the  manu- 
facture of  shot. 

442.  Plumbic  Monoxide,    PbnO.  —  This    substance    is 
found  native  as  lead-ochre,  a  yellow  massive  mineral  of 
crystalline  structure.     It  is  obtained  on  a  large  scale  by 
heating  lead  to  a  point  a  little  below  redness,  or  in  the 
process  of  cupellation.     The  former  product  is  known  as 
massicot,  the  latter  as  litharge.     Plumbic  monoxide  is  met 
with  in  several  isomeric  modifications,  as  a  yellow  or  red 
crystalline  substance,  or  as  an  amorphous   powder.      At 
a  red-heat  plumbic  monoxide  melts  to  a   clear,  dark-red 
liquid.     In  water  it  is  slightly  soluble  with  formation  of 
lead  hydrate.     Acids  dissolve   it   readily,  giving   rise   to 
plumbic  salts.     It  is  much  used  in  glass-making,  and  in 
glazing  earthen-ware.     Triplumbic  tetroxide  (Pb3O4),  (min- 
ium or  red  lead),  occurs  native,  and  is  formed  when  plum- 
bic monoxide  is  for  some  time  exposed  to  a  low  red  heat 
in  contact  with  air.     It  is  extensively  used  as  a  pigment, 
and  in  the  manufacture  of  flint-glass. 

443.  Plumbic   Carbonate,   PbCO3,TFAiYe   Lead.— This 
salt  it  found  beautifully  crystallized  in  Nature,  but  it  is 
largely  manufactured  as  a  paint.     It  is  produced  in  several 
ways,  but  the  following,   which  is  known  as  the  Dutch 
method,  is  considered  the  best :  Thin  sheets  of  lead,  rolled 
up  into  loose  scrolls,  are  placed  in  earthen  pots  with  weak 
vinegar  or  acetic  acid.      Thousands  of  these  pots,  fitted 
with  lead  covers  and  closely  packed,  are  then  buried  in 


250  DESCRIPTIVE   CHEMISTRY. 

spent  tan-bark.  The  acetic  acid  corrodes  the  metal,  form- 
ing a  superficial  coating  of  plumbic  acetate,  and  the  carbon 
dioxide  set  free  by  the  decomposing  vegetable  matter  de- 
composes the  acetate  with  formation  of  plumbic  carbonate 
and  free  acetic  acid.  The  acetic  acid  attacks  more  metal, 
which  is  again  converted  into  carbonate ;  and  thus,  with  a 
small  charge  of  vinegar,  the  operation  is  continued  a  long 
time,  and  a  large  quantity  of  lead  changed.  White  lead  is 
extensively  adulterated  with  baric  sulphate ;  it  may  be  de- 
tected by  adding  nitric  acid,  which  dissolves  the  lead, 
leaving  the  baric  sulphate  as  an  insoluble  residue. 

444.  Plumbic  Acetate,  Pb  (C3H3O2)2.  This  important 
salt  of  lead  is  easily  procured  by  dissolving  plumbic  mon- 
oxide (PbO)  in  acetic  acid.  It  receives  its  common  name 
"  sugar  of  lead  "  from  its  sweet  taste,  and  its  general  like- 
ness, in  appearance,  to  loaf-sugar.  It  is  exceedingly  poi- 
sonous. The  soluble  salts  of  lead  are  most  of  them  color- 
less, and  redden  litmus-paper.  Metallic  lead  is  easily  pre- 
cipitated from  solutions  of  its  salts  by  means  of  iron  or 
zinc. 


CHAPTER     XX. 

MAGNESIUM    GROUP MAGNESIUM,    ZINC,    CADMIUM. 

§  1.  Magnesium  and  its  Compounds. 

MAGNESIUM. — Symbol,  Mg.      Atomic  Weight,    24  ;    Quanti valence,  II. ; 
Specific  Gravity,  1.74. 

445.  History  and  Occurrence. — This  metal  was  first  ob- 
tained by  Davy,  in  1808.  It  does  not  occur  native,  but 
may  be  obtained  by  decomposing  magnesic  chloride  by 
metallic  sodium.  Magnesium  is  a  white  or  bluish-gray 
crystalline  metal ;  malleable  and  ductile,  melts  at  a  mod- 
erate red-heat,  and  volatilizes  at  higher  temperatures. 


ZIXC  AND   CADMIUM.  251 

Heated  in  the  air  it  burns  with  a  dazzling  bluish-white 
light,  and  is  on  this  account  much  used  for  signaling,  and, 
as  a  source  of  artificial  light  in  photography. 

446.  Magnesic  Oxide,  MgO,  Magnesia.— This  compound 
is  obtained  by  strongly  heating  magnesic  carbonate.     It  is 
a  white,  light  powder,  with  feeble  alkaline  properties,  very 
sparingly  soluble  in  water,  but  dissolving  readily  in  acids. 
It  is  found  native  as  the  mineral  periclase.     It  is  used 
principally  in  medicine  as  a  mild  aperient   and  antacid. 
Magnesic  Sulphate,  Mg  SO4  +  7H2O  (Epsom  Salts),  is  a 
common  ingredient  of  mineral  waters,  and  takes  its  name 
from  the  circumstance  of  its  being  contained  in  great  quan- 
tities in  the  springs  near  Epsom,  in  England.     The  com- 
mercial supply  is  chiefly  derived  from  sea-water,  by  de- 
composing the  magnesic  compounds  with  lime,  and  then 
adding   sulphuric   acid.      It   may  also   be    obtained    from 
magnesian  limestone.     It  is  soluble  in  water,  has  a  bitter, 
saline  taste,  and  is  used  in  medicine  as  a  cathartic  and  an 
antidote  to  various  poisons.     It  has  also  been  used  as  a 
fertilizer. 

§  2.  Zinc  and  Cadmium. 

ZINC. — Symbol,  Zn.    Atomic  Weight,  65  ;    Quantivalence,  II. ;  Molecular 
Weight,  65  ;  Molecular  Volume,  2  ;  Specific  Gravity,  7.0. 

447.  History  and   Occurrence.— This  element  is  not 
found  native,  but  is  obtained  on  a  very  extensive  scale  by 
the  decomposition  of  certain  ores,  among  which  zincic  sul- 
phide or  "blende"  (ZnS),  zincic  carbonate  (ZnCO3),  zincic 
oxide  (ZnO),  and  a  zincic  silicate,  are  the  most  important. 
It  is  a  brilliant,  bluish- white  metal.     At  common  tempera- 
tures it  is  brittle,  but,  when  heated  from  212°  to  300°  F.,  it 
may  be  rolled  out  into  thin  sheets,  and  retains  its  malle- 
ability when  cold.    At  400°  it  again  becomes  quite  brittle ; 
at  770°  it  melts,   and  at  a  red   heat  volatilizes.     When 
strongly  heated  in    the  air  it  takes  fire,   burning  with  a 
whitish-green  flame  and  production  of  zincic  oxide.     Zinc 


252  DESCRIPTIVE   CHEMISTRY. 

soon  tarnishes  in  a  moist  atmosphere,  forming  a  thin  film 
of  oxide,  which  resists  further  change.  This  property  ren- 
ders it  useful  for  a  variety  of  purposes,  such  as  for  gas- 
pipes,  gutters,  roofing,  and  for  galvanizing  iron,  thus 
preventing  it  from  oxidation.  It  is  also  used  in  the  prep- 
aration of  hydrogen  gas. 

448.  Zincic  Oxide,  ZnO. — This  compound  is  found  when 
zinc  is  burned  with  free  access  of  air.     It  is  a  fine  white 
powder,   familiarly  known  as  zinc  white.      It   is    largely 
used  as  a  paint,      Zincic    Chloride,    ZnCl2,  may  be  pre- 
pared by  distilling  an  intimate  mixture  of  zincic  sulphate 
and   sodic    chloride.      Zincic   chloride   is    a    whitish-gray 
translucent  substance,  soft  like  wax,  and  of  2.7  spec.  grav. 
It  melts  easily  and  distills  at  a  red  heat ;  it  is  deliques- 
cent, dissolves  easily  in  water  and  alcohol ;   has  a  burning 
taste,  and  is   poisonous.     It   is  used  in  various   chemical 
manufactures.     Wood,  impregnated  with  a  crude  solution 
of  zincic  chloride  known  under  the  name  of  "  Sir  William 
Burnett's  Fluid,"  is  effectually  preserved  from  decay,  this 
process   being  called  Burnettizing.     Zincic  sulphate,  Zn 
SO44-7H2O   (White  Vitriol),  may  be  prepared  either  by 
roasting  zincic  sulphide,  or  by  the  action  of  sulphuric  acid 
on  metallic  zinc.    It  strongly  resembles  magnesic  sulphate, 
and  is  used  in  medicine,  and  in  certain  operations  of  calico- 
printing. 

CADMIUM. — Symbol,  Cd.     Atomic  Weight,  112;  Quantivalence,  II. ;  Mo- 
lecular Weight,  112;  Molecular  Volume,  2;  Specific  Gravity,  8.6. 

449.  Cadmium. — This  metal  does  not  occur  native,  but 
may  be  obtained  from  ores  of  zinc,  and  from  some  of  the 
secondary  products  of  zinc-manufacture.     It  is  a  bluish- 
white,  strongly  lustrous  metal,  tarnishing  in  the  air.     It  is 
soft,  flexible,  malleable,  and  ductile,  melts  at  315°  C.,  is 
volatile,  and  crystallizes  from  the  fused  state,  in  regular 
octahedrons.     In  the  air  at  higher  temperatures  it  burns, 
cadmic  oxide  (CdO)  being  formed. 


IRON   AND   ITS  COMPOUNDS.  253 

CHAPTER    XXI. 

IRON,    MANGANESE,    NICKEL,    AND    COBALT. 

§  1.  Iron  and  its  Compounds. 

IRON. — Symbol,  Fe.  (Ferruni).    Atomic  Weight,  56  ;  Quantivalence,  II., 
IV.,  and  VI. ;  Specific  Gravity,  7.8. 

450.  History  and  Occurrence.— Were  we  to  seek  for 
that  circumstance  which  might  best  illustrate  the  peculiar- 
ities of  ancient  and  modern  civilization,  we  should  perhaps 
find  it  in  the  history  of  this  metal.      The  ancients,  imbued 
with  a  martial  spirit  and  passion  for  conquest,  made  iron 
the  symbol  of  war,  and  gave  it  the  emblem  of  Mars.     And 
if  it  were  required  also  to  symbolize  the  pacific  tendencies 
of  modern  society,  its  triumphs  of  industry  and  victories 
of  mind  over  matter,  its  artistic  achievements  and  scientific 
discoveries,  we  should  naturally  employ  the  same  metal, 
iron.     As  gold  and  jewels  have  long  been  the  type  of  bar- 
baric and  empty  pomp,  so  iron  may  now  be  well  regarded 
as  the  emblem  of  beneficent  and  intelligent  industry. 

Native  iron  of  meteoric  origin  has  frequently  been  found, 
and  instances  of  its  occurrence  on  the  earth  have  been 
reported,  but  usually  in  these  cases  the  iron  is  combined 
with  nickel.  We  are,  however,  acquainted  with  numerous 
ores  of  iron,  among  which  are  magnetite,  red  hematite, 
and  specular  iron,  brown  iron-stones,  spathic  iron,  and  clay 
iron-stone. 

451.  Preparation. — Metallic    iron  or  wrought-iron  has 
been  obtained  from  iron-ores,  and  to  some  extent  this  is 
still  its  source,  but  by  far  the  largest  portion  brought  into 
the  market  is  derived  from  the  decomposition  of  cast-iron, 
which  is  essentially  a  ferric  carbide,  but  also  contains  vary- 
ing quantities  of  other  substances.     The  operation  is  usu- 
ally conducted  in  reverberatory  furnaces.     In  this  process, 


254 


DESCRIPTIVE   CHEMISTRY. 


Fitt.  171. 


Puddling-Furnace. 


the  cast-iron  is  melted  on  a  flat  hearth  by  causing  the 
flame  to  impinge  upon  it  from  above  on  its  way  through 
the  furnace,  as  shown  in  Fig.  171.  A  workman,  with  a 
long,  oar-shaped  implement  of  iron,  stirs  (puddles)  the 
melted  mass  until  the  carbon  and  other  impurities  of  a  like 

nature  are  burned  away  or  con- 
verted into  a  slag,  and  the  met- 
al becomes  thick  and  pasty. 
This  is  called  puddling.  The 
puddler  then  rolls  up  from  the 
mass  a  ball  of  about  75  Ibs. 
weight,  which  he  transfers  to 
the  tilting  or  trip  hammer, 
where  it  is  beaten  by  heavy 
blows  into  a  crude  bar.  By 
this  operation  the  liquid  slag, 
consisting  chiefly  of  ferrous  silicate,  is  squeezed  out,  as 
water  is  expelled  from  a  compressed  sponge.  The  metal, 
still  hot,  is  then  passed  between  grooved  cylinders,  where 
it  is  rolled  out  into  bar-iron.  The  quality  of  metal  is 
greatly  improved  when  these  bars  are  broken  up,  bound 
together,  reheated  to  the  welding-point,  and  again  passed 
through  the  rolling-mill.  This  latter  operation  is  often 
repeated  several  times,  and  is  known  as  piling  OY  fagoting. 
452.  Properties. — Pure  iron  is  of  a  silver-white  color, 
while  ordinary  wrought-iron  is  grayish-white,  and  when 
polished  has  a  perfect  lustre.  In  the  absence  of  im- 
purities, iron  is  so  malleable  that  books  have  been  made 
of  it  with  leaves  as  thin  as  paper,  and  so  ductile  that 
it  may  be  drawn  out  into  wires  as  thin  as  a  hair.  Its 
most  useful  quality,  however,  is  its  superior  tenacity,  or 
power  of  resisting  strain ;  no  other  metal  being  equal  to 
it  in  this  respect.  Hence  the  value  of  iron  in  the  manu- 
facture of  cannons  and  mortars,  where  the  immense  ex- 
pansive force  of  gunpowder  is  to  be  resisted,  and  in  the 
making  of  wire  cables  for  suspension  bridges.  So  great  is 


IRON  AND   ITS  COMPOUNDS.  355 

its  tenacity  that  an  iron  wire  0.075  of  an  inch  in  diameter 
is  capable  of  supporting  a  weight  of  449  pounds. 

Wrought-iron  has  a  fibrous  text- 
ure, and  rough,  hackly  fracture,  Fig. 
172.  It  is  said  that  the  effect  of  con- 
stant jarring  is  to  cause  it  to  lose 
this  tough,  fibrous  character,  and  to 
become  crystalline.  It  usually  con- 
tains a  small  quantity  of  carbon,  which 
hardens  the  iron  without  affecting  its 
other  properties  to  any  great  extent ; 

,      .•£**  Texture  of  Wrought-Iron. 

but  if  the  amount  exceeds  £  per  cent., 

it  renders  the  iron  cold-short,  that  is,  brittle  and  liable  to 
snap  asunder  when  cold.  The  presence  of  sulphur,  even  in 
so  small  a  proportion  as  y^Vor?  unfits  tne  iron  f°r  being 
worked  at  a  red  heat,  as  it  is  liable  to  split  when  ham- 
mered ;  it  is  then  said  to  be  hot-short. 

453.  When  w rough t-iron  is  heated  to  whiteness,  it  be- 
comes soft,  pasty,  and  adhesive,  and  two  pieces  in  this 
condition  may  be  incorporated,  or  hammered  into  one. 
This  is  called  welding.  During  the  heating  a  film  of  triferric 
tetroxide  is  formed  upon  the  surface  of  the  metal,  which 
would  obstruct  the  ready  cohesion  of  the  separate  masses. 
To  prevent  this,  the  smith  sprinkles  a  little  sand  upon  the 
hot  iron,  which  gives  rise  to  the  formation  of  a  fusible 
silicate,  easily  forced  out  by  pressure,  leaving  clean  sur- 
faces that  unite  without  difficulty.  This  important  quality 
is  possessed  only  by  iron,  platinum,  and  sodium.  All  the 
other  metals  pass  suddenly  from  the  solid  to  the  liquid 
state,  at  their  respective  melting-points.  In  its  ordinary 
condition  iron  oxidizes  rapidly  in  the  air,  and  dissolves  in 
nitric  acid.  But  under  several  circumstances  it  assumes 
different,  and  peculiar  chemical  relations.  If  momen 
tarily  immersed  in  a  strong  mixture  of  nitric  and  sul- 
phuric acids  it  retains  its  metallic  lustre,  but  has  lost  the 
power  of  either  being  oxidized  in  the  air  or  of  dissolving 


256 


DESCRIPTIVE   CHEMISTRY. 


in  ni'ric  acid;  it  has  become  passive,  or  assumed  an  allo- 
tropic  form. 

454.  Uses — Iron    in   some   of   its    innumerable   forms 
ministers  to  the  benefit  of  all.     The  implements  of  the 
miner,  the  farmer,  the  carpenter,  the  mason,  the  smith,  the 
shipwright,  are  made  of  iron  and  with  iron.     Roads  of  iron, 
traveled  by  iron  steeds,  which  drag  whole  townships  after 
them  and  outstrip  the  birds,  have  become  our  commonest 
highways.     Ponderous  iron  ships  are  afloat  upon  the  ocean, 
with  massive  iron  engines  to  propel  them ;  iron  anchors  to 
stay  them  in    storms;  iron  needles  to  guide  them,  and 
springs  of  iron  in  chronometers  by  which  they  measure  the 
time.    Ink,  pens,  and  printing-presses,  by  which  knowledge 
is  scattered  over  the  world,  are  alike  made  from  iron. 

455.  Ferric  Carbides  (Cast-Iron}. —  As  already  stated, 
most  of  the  wrought  iron  of  commerce  is  obtained  from  the 
ore  indirectly,  the  latter  being  first  decomposed  in  such  a 
manner  as  to  yield  certain  ferric  carbides,  etc.,  known  as 
cast  or  pig-iron. 

The  operation  is  conducted  in  tall  chimney-like  struct- 
ures, termed  blast  -  furnaces. 
They  are  constructed  of  stone, 
and  lined  with  the  most  re- 
fractory fire-brick,  having  the 
form  seen  in  Fig.  173.  The  top 
or  mouth  of  the  furnace  serves 
for  charging  it,  and  for  the  es- 
cape of  smoke ;  it  is  both  door 
and  chimne^v.  The  tubes  or  tu- 
yere pipes  at  the  bottom  serve 
to  supply  the  air,  which  is  forced 
in  by  means  of  immense  blow- 
ing cylinders  driven  by  water 
or  steam  power.  The  amount 
of  air  thus  forced  through  some 
Smeiting-Furnace.  large  furnaces  exceeds  12,000 


FIG.  173. 


IRON   AND  ITS  COMPOUNDS.  £57 

cubic  feet  per  minute.  Formerly  the  air  was  used  at  the 
ordinary  temperature  (cold  blast),  but  within  a  few  decades 
an  immense  improvement  has  been  effected  by  heating  the 
air  before  it  enters  the  furnace  (hot  blast). 

456.  In  some  cases  the  materials  are  drawn  up  an  in- 
clined plane  to  the  mouth  of  the  shaft  by  the  same  engine 
that  impels  the  blast  mechanism.     The  furnace  is  supplied 
with  ore,  coal,  and  limestone,  broken  into  small  fragments. 
When  the  heat  is  sufficiently  intense  the  carbon  of  the  fuel 
deoxidizes  the  iron,  and  the  limestone  being  decomposed 
into  carbonic  dioxide  gas,  which  escapes,  and  "  burnt  lime," 
which  in  its  turn  acts  upon  the  ore,  unites  with  the  sand, 
clay,  silica,  and  other  impurities,  to  form  a  slag  or  scoria,  a 
crude  semi-vitreous,  easily-fusible  product.      The  melted 
cast-iron,  falling  to  the  bottom  of  the 

furnace,  accumulates  and  is  drawn  off 
by  taking  out  a  tap  or  plug.  It  is  al- 
lowed to  run  into  a  bed  of  sand,  con- 
taining straight  channels  and  furrows 
running  at  right  angles.  The  former 
are  called  by  the  workmen  the  sow,  and 
the  latter  the  pigs;  hence  the  term  Texture  of  Cast-iron. 
pig-iron.  As  the  contents  of  the  furnace  are  removed  from 
below,  crude-ore,  limestone,  and  fuel  are  constantly  supplied 
from  above,  and  the  operation  goes  on  day  and  night  un- 
interruptedly for  a  course  of  years,  or  until  the  fabric 
demands  repair. 

457.  Cast-iron  has  a  granular  texture  (Fig.  174),  and 
is  so  brittle  that  it  cannot  be  forged,  but  may  be  remelted 
and  cast  into  moulds.     It  expands  when  first  poured  into 
the  mould,  so  as  to  copy  it  perfectly,  but  subsequently 
contracts.      The  expansion  is  caused  by  the  particles  as- 
suming a  crystalline  arrangement  while  consolidating ;  the 
contraction  by  the  cooling  of  the  metallic  mass  when  solidi- 
fied.   There  are  several  varieties  of  cast-iron.    The  so-called 
"  Spiegeleisen  "  (mirror-iron)  of  Germany  is  a  nearly  pure 


258  DESCRIPTIVE   CHEMISTRY. 

tetraferric  carbide,  Fe4C.  Other  varieties  appear  to  be 
mixtures  of  this  compound  with  artificial  plumbago  (a 
variety  of  carbon),  or  with  true  metallic  iron. 

458,  Steel. — This  is  a  compound  of  the  metal  with  about 
one  and  a  half  per  cent,  of  carbon.     It  is  produced  in  dif- 
ferent ways.     One  variety  is  made  by  imbedding  bars  of 
the  best  wrought-iron  in  powdered  charcoal,  in  boxes  or 
sand-furnaces,  which  exclude  the  air,  and  heating  it  in- 
tensely for  a  week  or  ten  days.     The  chemical  changes  are 
obscure;   probably  carbonic  oxide  penetrates  the  heated 
metal,  is  decomposed,  surrenders  part  of  its  carbon  and 
escapes  as  carbonic  dioxide.     The  steel  when  withdrawn 
has  a  peculiar  rough,  blistered  appearance,  and  is  therefore 
known  as  blistered  steel.     This  method  of  making  steel  is 
called  the  process  of  cementation.     When  this  quality  of 
steel  is  melted  and  cast  into  ingots,  it  constitutes  cast-steel. 

A  great  improvement  in  the  manufacture  of  steel  has 
been  introduced,  called  from  its  inventor  the  Bessemer 
process.  By  means  of  this,  steel  is  produced  directly  from 
the  cast-iron,  without  previous  casting  into  pigs.  The 
melted  cast-iron  is  run  from  the  shaft-furnace  into  egg- 
shaped  vessels  made  of  boiler-plate,  lined  with  tire-clay, 
which  are  termed  "converters."  An  intense  blast  of 
compressed  air  is  forced  into  the  molten  mass,  and  ten  to 
twenty-five  minutes  of  this  operation  suffice  to  decarbonize 
the  cast-iron  so  as  to  convert  it  into  steel,  or  wrought-iron, 
as  may  be  desired. 

459.  In  its  properties  steel,  combines  the  fusibility  of 
cast-iron  with  the  malleability  of  bar-iron.     Its  value  for 
cutting  instruments,  springs,  etc.,  depends  upon  its  quality 
of  being  tempered.     When  heated  to  redness  and  suddenly 
quenched  in  cold  water,  it  becomes  so  hard  as  to  scratch 
glass.     If  again  heated  and  cooled  slowly,  it  becomes  as 
soft  as  ordinary  iron,  and  between   these  two  conditions 
any  required  degree  of  hardness  can  be  obtained.     As  the 
metal  declines  in  temperature,  the  thin  film  of  oxide  upon 


IRON  AND   ITS  COMPOUNDS.  259 

its  surface  constantly  changes  its  color.  The  workmen  are 
guided  by  these  tints.  Thus  a  straw-color  indicates  the 
degree  of  hardness  for  razors ;  a  deep  blue  for  sword-blades, 
saws,  and  watch-springs.  Steel  receives  a  higher  polish 
than  iron,  and  has  less  tendency  to  rust.  Nitric  acid  placed 
upon  steel  corrodes  it,  and  leaves  the  carbon  as  a  dark-gray, 
stain;  hence  it  is  often  used  for  writing  and  ornamental 
shading  upon  this  metal. 

460.  Ferrous  Oxide,  FeO. — This  compound  is  not  found 
native,  but  is  obtained  when  ferrous  oxalate  is  heated  in  a 
close  vessel,  as  a  black  powder,  which  in  the  air  ignites 
spontaneously,  burning  to  ferric  oxide,  Fe2O3  (diferric  tri- 
oxide),  which  is  of  very  wide  distribution  as  the  minerals 
red  hematite  and  specular  iron,  from  which  a  large  propor- 
tion of  the  iron  of  trade  is  derived.     Red  hematite  is  mas- 
sive, earthy,  or  fibrous,  and  brick-red  in  color.     Specular 
iron  is  extensively  employed  under  the  names  of  colcothar 
and  jewelers'  rouge,  as  a  pigment,  and  for  polishing  jewel- 
ry, glass,  and  metallic  objects. 

461.  Triferric  Tetroxide,    Fe3O4,    Magnetic    Oxide  — 
This  substance  occurs  native  as  the  mineral  magnetite,  the 
most  valuable  of  the  ores  from  which   iron  is  produced. 
This  appears  as  a  black,  crystalline  powder,  in  Nature  it 
forms  large  masses,  and  is  frequently  found   in   distinct 
octahedral   crystals   of  considerable    size.      The    triferric 
tetroxide  is  strongly  magnetic,  and  the  black  oxide  which 
forms  on  iron  when  heated  in  aqueous  vapor  consists  of 
this  compound,  which  is  also  produced  by  the  combustion 
of  iron  in  oxygen  gas. 

462.  Ferric  Bisulphide,  FeS2. — This  compound  occurs 
native  in  two  isomeric  modifications,  one,  the  mineral  mar- 
casite,  the  other,  iron  pyrites.     Both  forms  are  widely  dis- 
tributed.       Iron   pyrites    crystallizes    in    cubes   or   other 
forms  of  the  monometric  system,  of  a  golden-yellow  color 
and  strong  metallic  lustre.     Heated  in  the  air,  iron  pyrites 
burns  with  evolution  of  sulphurous   oxide,  and  it  is  much 


260  DESCRIPTIVE   CHEMISTRY. 

used  in  the  manufacture  of  sulphuric  acid.  Sulphur  and 
copperas  are  also  obtained  from  it,  but  it  is  never  worked 
for  iron.  Marcasite  is  a  mineral  possessed  of  a  white  color 
and  metallic  lustre,  which  in  moist  air  decomposes  rapidly, 
with  formation  of  ferrous  sulphate  (FeSo4  +  7H2O)  and 
evolution  of  heat.  It  occurs  in  coal-beds,  and  sometimes 
causes  their  spontaneous  ignition. 

463.  Ferrous  Sulphate,  FeSo4  +  7H2O,  Green  Vitriol, 
Copperas. — This  salt  is  largely  manufactured  from  iron 
pyrites.  It  is  used  in  dyeing,  for  making  ink  and  Prussian 
blue,  and  in  medicine.  It  often  exists  in  soils  to  a  perni- 
cious extent,  but  is  decomposed  by  lime,  gypsum  being 
formed.  Ferrous  Carbonate,  FeCO3.  This  is  a  very  abun- 
dant mineral  known  as  spathic  iron.  It  is  grayish-white, 
opaque,  and  crystallizes  in  rhombohedrons.  When  found 
in  large  masses  it  constitutes  one  of  the  most  valuable 
iron-ores.  Steel  has  been  made  directly  from  it,  hence  it  is 
known  as  steel-ore. 

§  2.  Manganese,  Nickel,  and  Cobalt. 

MANGANESE. — Symbol,  Mn.      Atomic  Weight,   55 ;    Quantivalence,   II., 
IV.,  and  VI. ;  Specific  Gravity,  8. 

464. — This  metal  never  occurs  in  Nature,  but  can  be 
obtained  by  making  manganic  oxide  into  a  paste  with  oil 
and  lamp-black  and  heating  this  mixture  to  whiteness  in  a 
covered  crucible.  It  is  a  hard,  brittle  metal  of  a  grayish- 
white  color,  and  rapidly  oxidizes  when  exposed  to  the  air. 
It  is  best  preserved  in  naphtha.  Manganic  Dioxide, 
MnO2,  occurs  in  Nature  as  the  mineral  pyrolusite.  It  is  an 
iron-black  or  steel-gray,  brittle  substance,  crystallizing  in 
forms  of  the  trimetric  system.  It  is  mined  extensively, 
being  employed  in  the  manufacture  of  chlorine  and  bleach- 
ing-powders,  as  a  source  of  oxygen,  and  for  discharging 
the  brown  and  green  tints  of  glass. 

465.  Nickel  and  Cobalt. — These  two  metals  are  closely 


CHROMIUM  AND  ITS  COMPOUNDS.  261 

related  by  their  properties.  Their  atoms  have  identical 
weights,  and  their  reactions  are  so  similar  that  there  is 
difficulty  in  separating  one  from  the  other.  They  occur 
associated  together,  and  are  found  alloyed  with  the  iron  of 
meteoric  origin. 

They  may  be  obtained  by  the  decomposition  of  ores, 
chiefly  nickelic  and  cobaltic  arsenides,  sulphides,  and 
sulph-arsenides.  They  are  both  magnetic,  and  resemble 
iron  in  many  of  their  properties.  Nickel  is  a  silver-white, 
ductile  and  malleable  metal,  of  about  8.4  spec,  grav.,  not 
much  more  fusible  than  iron.  It  is  used  principally  in  the 
manufacture  of  german  silver,  of  coinage,  and  other  similar 
alloys.  Cobalt  is  a  reddish  or  grayish-white  metal,  of 
about  8.9  spec.  grav. ;  hard  and  somewhat  malleable  at  a 
red  heat.  It  has  not  been  applied  to  any  useful  purpose. 
Cobaltous  Chloride,  CoCl2  +  6H2O,  may  be  obtained  in 
ruby-red  octahedral  crystals  from  solutions  of  cobaltous 
oxide  or  carbonate,  in  hydric  chloride.  The  dilute  solution 
of  these  is  used  as  a  sympathetic  ink,  the  characters  writ- 
ten with  it  being  so  pale  as  to  be  invisible  till  warmed, 
when  they  appear  blue,  owing  to  the  formation  of  the  an- 
hydrous chloride  (CoCl2).  On  cooling,  they  absorb  moist- 
ure and  again  disappear. 


CHAPTER    XXn. 

CHROMIUM,    ALUMINIUM,    AND   THE    PLATINUM    GROUP. 

§  1.    Chromium  and  its  Compounds. 

CHROMIUM.— Symbol,  Cr.    Atomic  Weight,  52.5  ;  Quantivalence,  II.,  IV., 
and  VI. ;  Specific  Gravity,  6.8. 

466.  Occurrence. — This  metal  may  be  prepared  by  ex- 
posing chromic  compounds  to  intense  heat  in  a  current  of 
hydrogen  gas  or  by  fusing  its  oxide  with  charcoal  in  a 


262  DESCRIPTIVE   CHEMISTRY. 

charcoal-lined  crucible.  When  the  oxide  is  reduced  by 
carbon  the  metal  obtained  is  of  steel-gray  color,  exceed- 
ingly hard,  and  not  easily  fused.  Many  of  the  compounds 
have  a  brilliant  color  and  are  used  as  paints.  It  gives 
color  to  the  emerald. 

467,  Dichromic  Trioxide,  Cr2Os,  Chromic  Oxide.—  This 
compound  may  be  obtained,  by  strongly  heating  a  chromic 
hydrate,  as  a  bright-green  powder,  or  in  the  form  of  green- 
ish-black rhombohedral  crystals  of  metallic  lustre,  5.2  spec, 
grav.,  and  great  hardness.     It  is  used  in  coloring  glass  and 
porcelain,  and  also  in  ordinary  painting  under  the  name  of 

VI 

chrome-green.  Chromic  Trioxide^  CrO3,  is  obtained  in 
splendid  crimson  needle-shaped  crystals  often  an  inch  in 
length,  easily  soluble  in  water,  melting  at  190°  C.,  and  de- 
composing at  250°  C.  It  is  a  powerful  oxidizing  agent. 

§  2.  Aluminium  and  its  Compounds. 

ALUMINIUM. — Symbol,  Al.    Atomic  Weight,  27.5 ;  Quantivalence  (A12)VI ; 
Specific  Gravity,  2.5. 

468,  History. — This  important  metal  was  discovered  by 
the  German  chemist  Wohler  in  1827.      It  is  not   found 
native,  but  may  be  obtained  by  decomposing  either  the 
chloride  or  the  fluoride  with  metallic  sodium.     It  is  one  of 
the  most  abundant  elements,  being  the  metallic  base  of 
alumina,  which  forms  the  argillaceous  rocks,  beds  of  clay, 
and  a  large  proportion  of  granite.     It  is  a  shining,  white 
metal,  of  a  shade  between  silver  and  platinum,  harder  than 
zinc  and  of  remarkable  strength  and  stiffness.     It  resists, 
like  silver,  the  oxidizing  influence  of  moist  air,  melts  at  a 
still  lower  temperature  than  that  metal,  and,  pound  for 
pound,  occupies  four  times  its  space.     It  is  the  most  sonor- 
ous of  metals,  giving  forth  a  clear  musical  sound  when 
struck.     It  is  malleable  and  ductile  like  iron,  exceeds  it  in 
tenacity,  and  combines  with  carbon,  forming  a  east  metal, 
which  is  not  malleable. 


ALUMINIUM  AND   IIS  COMPOUNDS.  £63 

It  conducts  electricity  nearly  as  well  as  silver,  and 
unlike  silver  is  not  tarnished  by  hydric  sulphide.  Ni- 
tric and  sulphuric  acids,  when  cold,  do  not  act  upon 
this  metal.  It  dissolves  in  hydric  chloride,  forming  alu- 
minic  chloride,  and  in  potassic  or  sodic  hydrate  solu- 
tions with  production  of  corresponding  aluminates.  At 
present,  aluminium  is  principally  employed  in  the  manu- 
facture of  aluminium  bronze,  small  weights,  and  optical 
instruments. 

469.  Aluminic  Oxide,   A12O3,    Alumina. — This    com- 
pound is  found  native.     Crystallized  and  colored  by  chro- 
mic oxide  it  forms  the  ruby  and  sapphire,  which  rank  next 
to  the  diamond  in  hardness  and  value.     In  a  pur,-  massive 
form  it  is  known  as  corundum,  and  this  when  ground  con- 
stitutes emery.    It  may  be  artificially  prepared  by  heating 
aluminic  hydrate.    It  is  a  white  powder,  insoluble  in  water, 
inodorous  and  tasteless. 

470.  Aluminic  Silicates. — These  bodies  form  the  chief 
constituents  of  clays,  which  result  from  the  decomposition 
of  feldspathic  and  silicious  rocks,  and  are  the  basis  of  all 
kinds  of  pottery.     Their  adaptation  for  this  purpose  de- 
pends upon  their  plasticity  when  mixed  with  water,  the 
readiness  with  which  they  may  be  moulded,  and  also  upon 
their  capability  of  solidifying  when  exposed  to  a  high  heat. 
After  burning,  the  ware,  though  hard,  is  porous,  and  ab- 
sorbs water  with  avidity,  even  allowing  it  to  filter  through. 
To  prevent  this,  the  ware  is  covered  with  a  glassy  coating, 
or  glazed. 

471.  Porcelain  consists  of  a  mixture  of  decomposed 
feldspar  (called  kaolin),  silica,  and  a  small  proportion  of 
lime,  the  ingredients  being  carefully  selected,  and  thor- 
oughly ground  and   incorporated.      When   moulded   into 
the  proper  form,  the  articles  are  dried  and  subjected  to  a 
high  heat  in  a  furnace,  in  which  state  the  ware  is  called 
biscuit.     They  are  then  glazed  by  dipping  them  into  a 
solution   of  powdered  quartz  and  feldspar,   which,  when 

12 


264  DESCRIPTIVE   CHEMISTRY. 

heated,  fuses  into  the  ware,  giving  it  a  vitreous  coating 
which  adds  to  its  compactness  and  strength.  The  partial 
fusion  of  the  materials  gives  porcelain  the  beautiful  semi- 
transparency  which  distinguishes  it  from  earthen-ware.  In 
coloring  porcelain,  the  patterns  are  printed  on  paper  which 
is  applied  to  the  biscuit  while  the  color  is  still  moist. 
When  the  color  is  absorbed,  the  porcelain  is  subjected  to 
another  baking,  which  fixes  the  tint.  In  the  finer  kinds  of 
porcelain  the  colors  are  mixed  with  a  fusible  glaze,  and 
applied  with  a  hair  pencil.  Common  red  pottery  ware 
owes  its  color  to  ferric  oxide  (Fe2O3),  and  is  glazed  with  a 
preparation  of  clay  and  plumbic  oxide.  Vessels  thus 
coated  are  objectionable  for  domestic  use,  as  the  lead-glaze 
is  sometimes  dissolved  by  acids,  producing  poisonous 
effects.  Bricks  are  unglazed.  Stone-ware  is  a  coarse  kind 
of  porcelain  glazed  with  salt.  Fire-bricks,  muffles,  and 
Hessian  crucibles,  are  made  of  a  pure,  infusible  clay,  con- 
taining a  large  amount  of  silica.  The  beautiful  blue  pig- 
ment ultramarine  is  one  of  the  aluminic  silicates  supposed 
to  be  colored  by  a  sodic  sulpho-ferrate.  A  variety  of  clay 
known  as  fuller's-earth  is  also  used  to  remove  grease  from 
woolen  cloths.  t  iy 

472.  Potassio-Aluminic  Sulphate.  KA1S2O8  +  12H2O, 
Alum. — Small  quantities  of  this  important  salt  are  found 
native,  but  for  commercial  purposes  it  is  prepared  artifi- 
cially by  several  different  methods.  In  this  country  it  i/ 
formed  by  treating  alumina  or  clay  with  sulphuric  acid, 
and,  after  the  lapse  of  a  few  months,  adding  potassic  sul- 
phate or  carbonate.  The  whole  is  then  leached,  and  the 
alum  separated  from  the  solution  by  crystallization.  Alum 
is  used  .largely  for  purifying  and  preserving  skins,  for  mor- 
dants in  dyeing  and  calico-printing,  for  glazing  paper,  for 
hardening  and  whitening  tallow,  clarifying  liquors,  and  in 
medicine  as  an  astringent  and  caustic.  Wood  impregnated 
with  it  is  almost  incombustible.  Alum  has  a  sweetish, 
styptic  taste,  and  is  soluble  in  18  parts  of  cold  water,  or  in 


THE  PLATINUM   GROUP.  265 

its  own  weight  of  boiling  water,  the  solution  having  an 
acid  reaction.  When  heated,  alum  swells  up  into  a  light, 
puffy  condition,  at  the  same  time  giving  off  its  water  of 
crystallization,  and  leaving  a  wbite,  anhydrous,  infusible 
mass  known  as  burnt  alum. 

§  3.   The  Platinum  Group. 

PLATINUM. — Symbol,  Pt.     Atomic  Weight,  197 ;  Quantivalence,  II.  and 
IV. ;  Specific  Gravity,  21.5. 

473.  This   rare   metal   is   always   found   native,  and 
usually  associated  with  palladium,  rhodium,  and  iridium. 
It  also  occurs  alloyed  with  gold,  copper,  iron,  and  lead. 
Its  chief  sources  are  the  mines  of  Mexico,  Brazil,  and  the 
Ural  Mountains.    Platinum  is  of  a  grayish-white  color,  and 
closely  resembles  silver  in  appearance.     It  is  one  of  the 
heaviest  of  metals,  and  when  pure  it  scarcely  yields  in  malle- 
ability to  gold  and  silver;  is  very  ductile,  and  takes  a  good 
polish.     But  the  qualities  which  render  it  so  useful,  and  in 
some  cases  indispensable  to  the  chemist,  are  its  extreme 
difficulty  of  fusion  (being  unaffected  by  any  furnace  heat), 
and  the  perfect  manner  with  which  it  resists  the  action  of 
almost  all  acids.     It  does  not  oxidize  in  the  air  at  any 
temperature,  and  is  not  acted  upon  by  simple  acids.     It  is 
slowly  dissolved  by  aqua  regia.     We  have  already  alluded 
(259)  to  the  power  possessed  by  spongy  platinum  of  con- 
densing gases  and  causing  the  union  of  oxygen  and  hydro- 
gen.    Platinum-black  is  a  preparation  of  the  metal  in  a 
still  more  minute  state  of  subdivision,  and  has  the  property 
of  effecting  chemical  changes  more  energetically  than  plat- 
inum sponge.      It  may  be  produced  by  electrolyzing  a 
dilute  solution  of  the  metal. 

474.  Platinic  Tetrachloride,  PtCl4,  is  obtained  by  dis- 
solving platinum  in  aqua  regia  and  evaporating  the  solution 
over  the  water-bath.     It  is  a  brownish-red  substance,  solu- 
ble in  water  and  alcohol,  forming  a  reddish-yellow  solution. 


266  DESCRIPTIVE  CHEMISTRY. 

It  is  a  valuable  reagent  for  potassic,    rubidic,  and  caesic 
compounds. 

Rhodium,  Ruthenium,  Palladium,  Iridium,  and  Os- 
mium, are  rare  and  generally  found  associated  with  plati- 
num, which  they  resemble  both  in  appearance  and  prop- 
erties. 


CHAPTER    XXIII. 

TIN,    SILICON. 

§  1.   Tin  and  its  Compounds. 

TIN. — Symbol,  Sn.  (Stannum)     Atomic  Weight,  118 ;  Quantivalence,  II. 
and  IV. ;  Molecular  Weight  236  (?) ;  Specific  Gravity,  7.29. 

475.  History  and  Occurrence. — Tin  is  a  brilliant,  silver- 
white  metal,  which  has  been   found  native  only  in  small 
quantities,  and  in  few  localities.     It  is  obtained  on  a  large 
scale  by  the  decomposition  in  furnaces  of  various  ores,  of 
which  the  mineral  cassiterite  is  the  most  important.     It  is 
softer  than  gold,  slightly  ductile  and  very  malleable,  and 
may  be  beaten  into  leaves  one-fortieth   of  a   millimetre 
thick.     It  melts  at  442°  F.     The  peculiar  crackling  sound 
given  by  tin  when  bent  is  due  to  a  disturbance  of  its  crys- 
talline structure.     It  tarnishes  but  slightly  on  exposure  to 
the  air  or  moisture,   and   is  therefore  very  valuable  for 
domestic  utensils.     This  propertv  also  renders  it  useful  for 
coating   other   metals   to    prevent    them    from    oxidizing. 
Sheet-iron  coated  with  tin,  with  which  it  forms  an  alloy, 
constitutes  common  tin-ware. 

476.  Stannic  Dioxide,  SnO2,  Oxide  of  Tin. — This  com- 
pound exists  in  several  modifications.     It  is  found  native, 
as  the  mineral  cassiterite,  in  broad  square  prismatic  crystals. 
More  or  less  rounded  by  attrition,  these  crystals  are  met 
with  in  the  alluvi.il  deposits  of  rivers  forming  "stream-tin," 


SILICON  AND   ITS   COMPOUNDS.  267 

from  which  metallic  tin  is  obtained.  Another  modification 
may  be  obtained  in  the  form  of  colorless  prisms  of  the 
trimetric  system,  which  are  very  hard  and  brilliant.  Stan- 
nic dioxide  is  much  used  in  the  manufacture  of  enamels 
and  opaque  glasses.  Britannia  metal  is  a  white  alloy 
much  resembling  German-silver  in  appearance.  It  consists 
chiefly  of  tin  and  antimony  in  the  proportion  of  9  parts  of 
the  former  to  1  part  of  the  latter. 

Titanium,  Zirconium,  Thorium,  are  but  little  known 
and  comparatively  unimportant.  They  are  allied  to  tin  by 
many  of  their  properties. 

§  2.  Silicon  and  its  Compounds. 

SILICON. — Symbol,  Si.    Atomic  Weight,  28  ;  Quantivalence,  IV. ;  Molec- 
ular Weight  56(?);  Molecular  Volume,  2;  Specific  Gravity,  2.49. 

477.  Silicon. — This  element  is  never  found  native,  but 
may  be  prepared  by  decomposing  silicic  fluoride  or  chloride 
with  sodium  or  aluminium.     It  has  three  allotropic  states : 
first,  amorphous  silicon — a  brown  powder;  second,  a  crys- 
talline hexagonal  variety  resembling  graphite;  and  a  third, 
octahedral  form  which  is  exceedingly  hard.     It  is  of  no 
importance  except  to  the  scientific  chemist. 

478.  Silicic  Dioxide,  SiO2,  Silica. — This   compound  is 
one  of  the  most  important  and  widely-distributed  of  sub 
stances ;  forming  the   bulk  of  the  minerals,  quartz,  flint, 
agate,  chalcedony,  opal,  etc.,  and  of  most  sandstones,  and 
sandy  soils.    It  is  also  an  essential  and  sometimes  predom- 
inating ingredient  in  granite,  and  many  other  rocks.     It 
exists    in    two   modifications:    one    crystalline,   the   other 
amorphous.     In  both  of  these  conditions  it  is  almost  infu- 
sible.    By  the  intense  heat  of  the  oxy-hydrogen  blow-pipe 
it  is  reduced  to  a  transparent  glass,  and  may  be  spun  out 
into  threads. 

Both  modifications  of  silica  are  insoluble  in  water,  and 
in  all  acids,  except  the  fluohydric,  but  it  is  dissolved  by  solu- 


268  DESCRIPTIVE   CHEMISTRY. 

tions  of  alkaline  silicates.  Hence,  all  natural  waters  which 
contain  alkaline  silicates  may  also  contain  a  little  silica. 
When  water  containing  even  small  quantities  of  alkaline 
carbonates  acts  upon  silica  under  pressure  and  at  tempera- 
tures from  300°  to  400°  C.,  it  is  capable  of  dissolving  a 
large  quantity  of  it,  which  is  again  deposited  when  the 
pressure  and  heat  are  removed.  This  is  the  cause  of  the 
siliceous  deposits  formed  by  certain  hot  springs,  as  the 
geysers  of  Iceland.  If  wood  be  present  in  such  waters,  as 
it  decays,  the  particles  of  silica  are  deposited  in  place  of 
those  that  escape,  and  thus  a  copy  of  the  wood  in  stone,  or 
a  petrifaction,  is  produced. 

479.  Crystalline  Modification. — This  is  found  in  Nature 
as  quartz,  amethyst,  etc.,  forming-  rhombohedra  or  hexag- 
onal crystals  terminated  by  six-sided   summits  (Fig.  175), 
which  are  sometimes  of  enormous  size.     It  is  very  hard, 
colorless  when  pure,  and  often  quite  transpar- 
ent.    The  amorphous  modification  of  silicic 
dioxide  is  a  pure  white  powder.     This  com- 
pound, with  varying  quantities  of  water  held 
hygroscopically,  constitutes  the  opal. 

480.  Silicic  Fluoride,  SiF4.  —  This  is  a 
colorless  gas  produced  when  hydric  fluoride 
acts  upon  silica.  When  passed  into  water 
the  g;as  is  decomposed,  with  formation  of  hy- 

Quartz-Crystal.        ,.%.  '  ,,  J 

dnc  silicate,  and  a  peculiar  compound  known 
as  hydric  fluo-silicate,  H,SiF6. 

Silicic  Acids. — If  to  a  solution  of  sodic  or  potassic 
silicate  hydric  chloride  be  added,  silicic  acid  separates  as  a 
transparent  jelly,  which  is  nearly  insoluble  in  water  or 
acids.  By  reversing  the  operation,  that  is,  by  pouring  the 
sodic,  etc.,  silicate  solution  into  the  hydric  chloride,  no  pre- 
cipitate results,  but  by  subjecting  this  mixture  to  dialysis  a 
clear  aqueous  solution  of  silicic  acid  may  be  obtained.  The 
exact  composition  of  these  hydric  silicates  is  not  known. 
This  gelatinous  state  may  be  continued  by  keeping  it 


SILICON   AND   ITS   COMPOUNDS.  269 

moist,  but  as  soon  as  it  is  deprived  of  water  it  falls  to  a 
gritty  powder. 

481.  Glass. — When  mixtures  of  pure  quartz-sand  with 
potash,  or  soda,  and  various  metallic  oxides,  are  strongly 
heated,  they  fuse  to  a  liquid,  which  on  being  gradually 
cooled  before  solidifying  passes  through  a  thick,  viscous, 
semi-fluid  condition.      While  in   this  s  ,ate  they  may  be 
moulded  into  any  desired  shape,  retaining  their  form  and 
transparency  when  cold.    Thus  we  have  a  compound  easily 
moulded  at  a  certain  stage  of  fusion,  uncry  stall  ine  when 
cold,  but  transparent,  hard,  strong,  insoluble,  and  durable — 
that  is,  common  glass.     The  materials  for  the  manufacture 
of  glass   are,   first,   pulverized    quartz    or   sand — for   the 
manufacture  of  the  finest  varieties  of  glass  a  pure  white 
sand  free  from  ferric  oxide  is  employed — second,  the  basic 
constituents,  potash,  soda,  lime,  magnesia,  and  lead-oxides 
more  or  less  pure,  according  to  the  quality  of  the  glass 
required.     Various  metallic  oxides  are  also  employed  as 
coloring  agents.     Thus  cupric  oxide  gives  a  green  color, 
gold  oxide  a  ruby,  uranic  oxide  a  yellow,  cobaltic  oxide  a 
deep-blue,  manganic  oxide  a  purple,  and  a  mixture  of  co- 
baltic and  manganic  oxides  a  black  glass.     Enamel  watch- 
dials  and  semi-opaque  transparencies  are  glass  rendered 
milk-white  by  stannic  oxide  or  bone  earth. 

482.  Varieties  of  Glass. — The  silicates  of  lime,  magne- 
sia, iron,  soda,  and  potash,  in  their  impure  form,  produce 
the  coarser  kinds  of  glass  of  which  green  bottles  are  made. 
The  silicates  of  soda  and  lime  give  the  common  window- 
glass  and  French  plate.     Lime  hardens  glass,  and  adds  to 
its  lustre;  soda  tends  to  give  it  a  greenish  tinge.     Bohe- 
mian glass,  the  most  beautiful  variety,  hard  and  highly  in- 
fusible, is  a  silicate  of  potash  and  lime.      Crystal  glass,  or 

flint  glass,  so  called  because  pulverized  flints  were  formerly 
used  in  making  it,  is  a  potassio-plumbic  silicate.  The  red 
plumbic  oxide  renders  it  very  soft,  so  as  to  be  easily 
scratched,  but  greatly  increases  its  transparency,  brilliancy, 


270  DESCRIPTIVE   CHEMISTRY. 

and  refractive  power.  Sometimes  the  proportion  of  oxide 
of  lead  used  rises  as  high  as  fifty-three  per  cent.  Glass  of 
this  composition  forms  what  is  called  paste,  and,  when 
suitably  cut,  is  used  to  imitate  the  diamond.  By  the  addi- 
tion of  a  trace  of  ferric  oxide  the  yellow  of  the  topaz  is 
imitated,  and  by  cobaltic  oxide  the  brilliant  blue  of  the 
sapphire  is  produced. 


CHAPTER    XXIV. 
Carbon  and  its  Compounds. 

CARBON. — Symbol,  C.  Atomic  Weight,  12  ;  Quantivalence,  II.  and  IV.  ; 
Molecular  Weight  24(?);  Molecular  Volume,  2;  Specific  Gravity 
(Diamond),  3.5. 

483.  History  and  Properties.—  Carbon,  from  the  Latin 
carbo,  coal,  is  the  name  applied  to  the  solid  with  which 
we  are  familiar  in  the  various  forms  of  charcoal,  min- 
eral coal,  lamp-black,  etc.  It  is  met  with  in  three  well- 
marked  allotropic  forms — the  diamond,  graphite,  and  char- 
coal. The  purest  form  of  carbon  is  the  diamond — a  very 
extraordinary  kind  of  matter.  It  crvstallizes  in  regular 
octahedrons  or  other  forms  of  the  monometric  system, 
the  faces  being  frequently  convex  (Figs.  176,  177,  and 
178),  and  is  the  hardest  body  known.  Diamonds  are 

FIG.  176.  FIG.  177.  FIG.  178. 


found  in  the  earth  in  various  places,  usually  in  the  form  of 
rounded  pebbles  covered  with  a  brownish  crust.     Of  their 


CARBON  AND  ITS  COMPOUNDS.         271 

mode  of  production  nothing  whatever  is  known.  The  finest 
specimens  are  perfectly  colorless  and  limpid,  but  they  are 
also  of  various  colors.  The  diamond  has  a  very  high 
refractive  and  dispersive  power  by  which  it  flashes  the 
most  varied  and  vivid  colors  of  light.  It  is  a  non-con- 
ductor of  electricity,  and  resists  the  action  of  all  known 
chemical  substances.  The  diamond  remains  unchanged  at 
a  very  high  degree  of  heat ;  but,  if  made  red-rot  and  car- 
ried into  pure  oxygen,  it  burns  with  a  steady  glow,  like  a 
little  star,  the  product  being  carbonic  dioxide.  From  its 
high  refractive  power,  resembling  in  this  respect  some  or- 
ganic substances,  Newton  predicted  that  it  would  prove 
not  only  combustible,  but  of  organic  origin.  This  view 
seems  to  be  supported  by  the  fact  that  the  crystal  on 
being  burned  leaves  a  trace  of  ash  in  the  form  of  a  cellu- 
lar net-work.  In  the  flame  of  the  voltaic  arc,  the  diamond 
becomes  white-hot,  swells,  and  is  converted  into  a  black, 
coke-like  mass.  The  diamond  is  the  most  brilliant  and 
precious  of  gems.  Being  a  powerful  refractor  of  light,  it 
has  been  sometimes  employed  for  the  lenses  of  micro- 
scopes, but  it  is  chiefly  used  for  cutting  glass  and  drilling 
apertures  through  other  gems. 

484.  Graphite,  or  Plumbago,  is  another  allotropic  form 
of  carbon.  It  is  found  in  rocks,  sometimes  in  considerable 
masses,  and  crystallizes  in  six-sided  plates 
of  a  metallic  lustre,  resembling  lead,  Fig. 
179;  hence  it  is  called  black-lead.  Its 
spec.  grav.  is  about.  2.1.  Like  the  dia- 
mond, it  resists  the  action  of  intense 
heat,  and  is  useful  to  the  chemist  in 
making  crucibles.  It  is  friable,  has  an  unc- 
tuous feel,  and  is  used  instead  of  oil  to 
relieve  the  friction  of  machinery.  It  is  unaffected  by  the 
weather,  and  hence  forms  a  valuable  coating  to  protect 
iron-work  from  rust;  and,  as  it  resists  heat,  it  is  fitted 
for  stove-polish.  It  is,  however,  often  adulterated  largely 


272  DESCRIPTIVE   CHEMISTRY. 

with  lamp-black,  which  may  be  detected  by  heating  the 
suspected  sample  to  redness,  when  the  lamp-black  burns 
away.  Its  most  important  use  is  in  the  manufacture  of 
pencils.  The  powder,  subjected  to  enormous  pressure, 
coheres  in  masses,  and  is  then  sawed  into  thin  slices,  and 
again  into  small  bars,  which  are  placed  in  grooved  cedar- 
sticks  for  use.  Though  apparently  so  soft,  the  particles 
of  graphite  are  extremely  hard,  and  soon  wear  out  the 
steel  saws  with  which  the  mass  is  cut. 

Graphite,  unlike  diamond,  may  be  artificially  produced. 
When  cast-iron,  which  has  been  melted  in  contact  with  an 
excess  of  carbon,  is  allowed  to  cool  slowly,  the  carbon 
crystallizes  out  in  the  form  of  graphite.  In  the  manufact- 
ure of  coal-gas,  a  layer  of  pure,  dense  carbon,  having  a 
metallic  lustre,  is  deposited  upon  the  hottest  parts  of  the 
retort.  It  is  called  gas-carbon,  and  seems  to  be  a  variety 
of  graphite,  if,  indeed,  it  be  not  itself  an  allotropic  form  of 
carbon. 

485.  Charcoal,  the  third  well-settled  allotropic  variety 
of  carbon,  is  obtained  when  any  organic  substance,  as 
wood,  bones,  or  sugar,  is  strongly  heated  or  burned  with  a 
partial  exclusion  of  air.  It  is  ordinarily  prepared  by  covering 
large  heaps  of  wood  with  ashes  or  turf,  and  burning  them 
with  a  restricted  supply  of  air,  so  as  to  prevent  complete 
combustion,  and  only  char  the  wood.  The  finer  kinds  of 
charcoal,  such  as  are  used  for  making  gunpowder,  are  pro- 
duced by  distilling  the  wood  in  close  iron  retorts.  Char- 
coal is  a  black,  brittle,  inodorous,  tasteless  solid;  a 
good  conductor  of  electricity,  but  a  bad  conductor  of 
heat,  and  perfectly  insoluble  in  all  liquids.  It  is  oxidized 
by  strong  hydric  nitrate,  but  resists  the  action  of  air  and 
moisture,  and  is,  therefore,  very  unchangeable.  The  tim- 
bers, and  grains  of  wheat  and  rye,  converted  into  charcoal 
eighteen  hundred  years  ago,  at  Herculaneum,  remain  as 
entire  as  if  they  had  been  charred  but  yesterday.  Wooden 
posts  are  rendered  more  durable  by  charring  their  ends 


CARBON   AND  ITS  COMPOUNDS.  273 

before  placing  them  in  the  ground.  The  interiors  of  tubs 
and  casks  are  often  charred  for  the  same  reason. 

486.  Uses. — The  chief  use  of  charcoal  is  as  a  fuel. 
When  pure,  it  burns  without  flame,  although  it  usually 
contains  water  which,  during  the  combustion,  is  partially 
decomposed  and  hydric  carbide  is  foinaed  which  burns  with 
a  slight  flame.  A  cubic  foot  of  charcoal  from  soft  wood 
weighs  from  8  to  9  Ibs.  ;  from  hard  wood,  from  12  to  13  Ibs.  ; 
hence,  hard-wood  coal  is  best  adapted  to  produce  a  high 
heat  in  a  small  space.  At  high  temperatures,  charcoal  has 
a  very  powerful  affinity  for  oxygen  ;  therefore,  it  is  of  great 
value  in  reducing  metals  from  their  oxides,  in  the  smelting- 
furnace. 

Having  the  structure  of  the  wood  from  which  it  was 
derived,  charcoal  is  very  porous,  and  possesses  in  a  remark- 
able degree  the  power  of  absorbing  gases,  and  condensing 
them  within  its  pores.  It  will  absorb  90  times  its  bulk  of 
ammonia ;  35  times  its  bulk  of  carbonic  dioxide ;  and  9 
times  its  bulk  of  oxygen.  Freshly-burned  charcoal  im- 
bibes watery  vapor  from  the  air  very  greedily,  and  by  a 
week's  exposure  increases  in  weight  from  10  to  20  per 
cent.  Charcoal,  having  the  finest  pores,  possesses  this 
power  of  absorption  in  the  greatest  degree ;  the  spongy 
sort  least.  "  A  cubic  inch  of  charcoal,"  says  Liebig,  "  must 
have,  at  the  least  computation,  a  surface  of  100  square 
feet."  Charcoal  absorbs  noxious  gases  and  offensive  odors ; 
and,  when  crushed,  foul  water  filtered  through  it,  and 
tainted  meat  packed  in  it,  are  restored  to  sweetness.  The 
charcoal  from  bones  (bone-black)  is  superior  to  wood-char- 
coal for  purifying  purposes.  It  is  extensively  used  in 
sugar  refineries  to  decolorize  syrups.  Vinegars,  wines, 
etc.,  are  bleached  in  the  same  way. 

Charcoal  is  a  powerful  deodorizer  and  disinfectant,  but 
it  is  not  an  antiseptic,  or  preventer  of  change,  as  has 
been  supposed.  In  fact,  it  is  an  accelerator  of  decomposi- 
tion. It  was  formerly  thought  that  charcoal  acted  by 


274  DESCRIPTIVE   CHEMISTRY. 

simply  sponging  up  the  deleterious  gases,  and  retaining 
them  in  its  pores ;  but  it  has  been  lately  shown  that,  by 
means  of  its  condensing  power,  it  is  a  powerful  agent  of 
destructive  change.  The  condensed  oxygen  seizes  upon 
the  other  gases  present,  and,  oxidizing  them,  forms  new 
products.  It  thus  changes  ammonia  to  hydric  nitrate,  and 
hydric  sulphide  to  hydric  sulphate.  The  body  of  a  dead 
animal  packed  in  charcoal  emits  no  odor,  but,  instead  of 
being  preserved,  its  decomposition  is  much  hastened.  This 
property  has  been  made  medically  available  in  the  form  of 
charcoal-poultice,  to  aid  in  the  removal  of  sloughing  and 
gangrenous  flesh  in  malignant  wounds  and  sores.  Lamp- 
black is  an  impure  variety  of  charcoal.  It  is  the  soot  de- 
posited from  the  burning  of  pitchy  and  tarry  combustibles. 
The  smoke  is  conducted  through  long  horizontal  flues  ter- 
minating in  chambers  hung  with  sacking,  upon  which  the 
lamp-black  is  deposited.  It  is  used  for  making  printers' 
ink  and  black  paint. 

487.  Carbonic  Monoxide,  CO,  Carbonic  Oxide,  is  a 
colorless,  almost  inodorous  gas,  which  burns  with  a  pale- 
blue  flame.  It  is  produced  by  burning  carbon  with  an  im- 
perfect supply  of  air,  and  its  formation  may  be  observed  in 
an  open  coal-fire.  At  the  lower  part  of  the  grate,  where 
the  air  is  abundant,  carbonic  dioxide  is  formed.  As  it 
ascends  into  the  hot  mass  above,  it  loses  half  of  its  oxygen, 
becoming  carbonic  monoxide.  The  liberated  oxj-gen,  com- 
bining with  the  carbon  of  the  fuel,  also  produces  an  equal 
quantity  of  the  gas.  As  the  carbonic  monoxide  thus 
formed  rises  to  the  surface  of  the  fire,  it  burns  to  carbonic 
dioxide,  with  a  lambent,  blue  flame.  This  gas  may  be  ob- 
tained pure  and  in  great  quantities  by  heating  1  part  of 
potassic  ferrocyanide  with  10  of  hydric  sulphate  in  a  capa- 
cious retort.  Carbonic  monoxide,  when  respired,  acts  as  a 
violent  poison.  Even  when  mixed  with  a  very  large  quan- 
tity of  air  its  inhalation  produces  giddiness  and  headache, 
and  has  in  many  instances  proved  fatal. 


CARBON  AND   ITS   COMPOUNDS.  275 

488.  Carbonic  Dioxide,  COS,    Carbonic  Acid.  —  This 
compound  was  discovered  by  Van  Helmont  about  the  be- 
ginning of  the  seventeenth  century.     It  is  a  normal  con- 
stituent of  the  atmosphere,  to  the  average  amount  of  4 
volumes  in  10,000.     Wherever  carbon  in  any  of  its  modifi- 
cations, or  any  carbonic  compounds,  burn,  with  free  access 
of  air,  carbonic  dioxide  is  produced.     The  combustion  of  a 
bushel  of  charcoal  produces  2,500  gallons  of  the  gas.     It 
is  produced  by  fermentation,  and  the  slow  decomposition 
of  organic  bodies,  and  also  by  the  respiration  of  animals. 
Each  adult  man   exhales  about  140  gallons  per  day.     It 
is  also  produced   by  chemical  changes  which  take  place 
in  the  interior  of  the  earth,  and  it  comes  up  with  the  waters 
which  rise  to  the  surface.     In  volcanic  regions  it  is  occa- 
sionally met  with,  unmixed  with  other  gases.     Rising  to 
the  surface,  often  more  rapidly  than  it  is  diffused  into  the 
air,  it  accumulates  in  invisible  pools  and  ponds.     Through 
the  celebrated  Grotto  del  Cane,  in  Italy,  a  man  may  walk 
unharmed,  but  a  dog  with  its  nostrils  near  the  earth  is  suffo- 
cated on  entering.     The  poison  valley  of  Java  is  a  lake  of 
carbonic  dioxide  filled  with  the  bleached  bones  of  dead 
animals. 

489.  Preparation. — Carbonic  dioxide  is  most  conven- 
iently obtained  by  the  action  of  an  acid  upon  small  frag- 
ments  of  marble,  limestone,  or  chalk.    Any  strong   acid 
will  answer  the  purpose,  but  hydric  chloride  is  the  best. 
The  powdered  mineral  is  placed  in  a  jar  and  covered  with 
water.     A  little  dilute  acid  is  then  poured  down  through 
the  tube,  Fig.  180.  Effervescence  immediately  takes  place, 
and  the  gas  escapes  through  the  bent  tube.     It  may  be 
collected  over  water  in  the  pneumatic  trough,  or,  as  it  is 
heavier  than  the  air,  it  will  quickly  displace  it  in  an  open 
vessel.     The  change  is  thus  shown : 

CaC03  +  2HC1  =  CaCl,  +  H3O  +  CO,. 
A  cubic  inch  of  marble  will  yield  four  gallons  of  the  gas. 


276 


DESCRIPTIVE   CHEMISTRY. 


FIG.  180. 


Jar  for  generating  Carbonic  Dioxide. 


490,  Properties, — Carbonic  dioxide  is,  at  ordinary  tem- 
peratures and  pressures,  a  colorless,  inodorous  gas,  of  1.52 

specific  gravity.  It 
does  not  support 
combustion.  To 
prove  this,  and  to 
show  also  that  it  is 
heavier  than  air,  we 
have  but  to  place 
a  lighted  taper  in  a 
jar,  and  pour  in 
carbonic  dioxide 
from  another  ves- 
sel, Fig.  181;  the 
invisible  current 
promptly  puts  out 
the  light. 

When  respired, 
carbonic  dioxide  is  fatal  to  life.  If  pure,  it  produces  spasm 
of  the  glottis,  closes  the  air-passages,  and  thus  kills  sud- 
denly by  suffocation;  but,  though  it  has  been  held  that 
carbonic  dioxide  exerts  a  poisonous 
action,  it  is  more  probable  that  these 
effects  a  re  merely  due  to  deprivation 
of  oxygen.  This  gas  often  accumu- 
lates at  the  bottom  of  wells,  and  in 
cellars,  stifling  those  who  may  un- 
warily descend.  To  test  its  pres- 
ence in  such  cases,  it  is  common  to 
lower  a  lighted  candle  into  the  sus- 
pected place,  and,  if  it  is  not  extin- 
guished, the  air  may  be  breathed 
safely  for  a  short  time.  If  the  light  goes  out,  it  will  be  ne- 
cessary before  descending  to  let  down  dry-slacked  lime, 
or  pans  of  freshly-burned  charcoal,  to  absorb  the  gas. 
When  carbonic  dioxide  is  brought  into  contact  with 


FIG.  181. 


Pouring  Carbonic  Acid. 


CARBON  AND  ITS  COMPOUNDS.         277 

calcic  hydrate  solution  (lime-water),  the  liquid  turns  milky, 
from  the  production  of  calcic  carb  juate.  Thus,  if  we 
expose  a  saucer  of  lime  water  to  the  air,  in  a  short  time  its 
surface  is  covered  with  a  thin  film  of  calcic  carbonate, 
proving  that  there  is  carbonic  dioxide  in  the  atmosphere. 
If  we  blow  through  a  tube  into  a  jar  of  lime-water,  it  quickly 
becomes  turbid  from  the  same  cause,  thus  showing  that 
there  is  carbonic  dioxide  in  the  expired  breath.  Under  a 
pressure  of  36  atmospheres  at  32°  F.,  carbonic  dioxide 
shrinks  into  a  colorless,  limpid  liquid  lighter  than  water. 
When  this  pressure  is  removed,  it  does  not  suddenly 
resume  its  gaseous  state,  but  evaporates  with  such  ra- 
pidity, that  one  portion  absorbs  heat  from  another,  and 
freezes  it  to  a  white  solid,  like  dry  snow.  This  solid  car- 
bonic dioxide  wastes  away  but  slowly,  and  may  be  handled, 
though,  if  it  rests  long  upon  the  skin,  it  disorganizes  it  like 
red-hot  iron. 

491.  Uses. — The  sparkling  appearance  and  lively,  pun- 
gent taste  of  various  mineral  waters  are  due  to  the  carbonic 
dioxide  they  contain.  Water  absorbs  nearly  its  own 
volume  of  carbonic  dioxide,  but  by  means  of  a  forcing-pump 
it  may  be  made  to  receive  a  much  larger  proportion.  "  Soda- 
water  "  is,  ordinarily,  only  water  charged  with  carbonic  di- 
oxide. Being  overcharged,  when  the  pressure  is  withdrawn, 
the  gas  escapes  with  violent  effervescence.  The  effect  is 
the  same  whether  the  carbonic  dioxide  is  forced  into  the 
water  from  without,  or  generated  in  a  tight  vessel,  as  is 
the  case  with  fermented  liquors;  the  gas  gradually  formed 
is  dissolved  by  the  water,  and,  escaping  when  the  cork  is 
withdrawn,  produces  the  fuming  and  briskness  of  the 
liquor. 

Carbonic  dioxide  is  also  used  to  extinguish  fires.  In 
one  case  an  English  coal-mine,  which  had  been  on  fire 
thirty  years,  was  completely  extinguished  by  pouring  into 
it  eight  million  cubic  feet  of  this  gas.  In  the  "  fire- 
annihilators "  or  "  extinguishers,"  the  gas  is  generated  at 


278  DESCRIPTIVE   CHEMISTRY. 

the  time  when  wanted,  in  a  suitably-constructed  metallic 
vessel,  and  discharged  into  the  fire  under  pressure. 

492.  Carbonic  Bisulphide,  CS2. — This  is  a  very  volatile, 
colorless  liquid,  of  about  1.27  specific  gravity,  which  boils  at 
118.5°  F.     It  has  a  peculiar,  very  unpleasant  odor  and  pun- 
gent taste.     It  lias  never  been  frozen,  and  is  used  in  ther- 
mometers which  are  to  measure  very  intense  degrees  of 
cold.     It  is  highly  inflammable,  burning  with  a  blue  flame, 
and  yielding  carbonic  dioxide  and  hydric  sulphate.     It  dis- 
solves sulphur,  phosphorus,  and  iodine,  and  is  dissolved  in 
ether,  but  not  in  water.     It  is  produced  by  bringing  vapor 
of  sulphur  into  contact  with  red-hot  charcoal,  the  compound 
vapor  being  condensed  in  cold  vessels.     From  its  high  dis- 
persive power  over  light,  it  is  used  to  fill  hollow  prisms  of 
glass  for  spectroscopic  observations.     It  is  also  applied  in 
chemical  manufactures,  to  a  variety  of  purposes. 

493.  Cyanogen,  C2N2. — This  substance  may  be  best  pro- 
cured by  heating  mercuric  cyanide   (HgC2N2)  in  a  glass 
tube  or  retort.      The  compound  is  decomposed,  the  cyano- 
gen being  evolved  as  a  colorless  gas,  which 
may  be  ignited,  burning  with  a  beautiful 
blue  flame,  edged   with  purple,  Fig.  182. 
Cyanogen  is   a  transparent,  colorless  gas, 
poisonous   if   respired,  and   with   a    strong 
odor.     It  is  very  soluble  in  water,  and  hence 
must  be  collected  in  the  pneumatic  trough 
over  mercury.     It  is  reduced  to  a  colorless, 
limpid  liquid  by  a  pressure  of  four  atmos- 
pheres, and  freezes  into  a  transparent  crys- 
talline solid  at  30°  C. 

cyanogen.  «*•  Hydric  Cyanide,  HCN  (Prussic 
Acid). — This  substance  is  found,  in  very 
small  quantities,  in  the  leaves,  bark,  blossoms,  and  fruit  of 
the  peach,  cherry,  sloe,  and  many  other  plants.  It  is  best 
obtained  by  the  decomposition  of  various  metallic  cyanides 
with  a  strong  acid,  and  subjecting  the  mixture  to  distilla- 


COMBUSTION.  279 

tion.  Hydric  cyanide,  when  pure,  is  at  common  tempera- 
tures a  colorless  liquid,  which  solidifies  at  15°  C.,  and 
boils  at  26°  C.  It  has  the  peculiar  odor  of  bitter  almonds 
or  peach-blossoms.  It  is  exceedingly  poisonous,  one  drop 
producing  instant  insensibility,  and  almost  instant  death. 
The  inhalation  of  the  vapor  should,  therefore,  be  most 
carefully  guarded  against.  The  prussic  acid  of  the  shops 
is  a  more  or  less  dilute  solution  of  hydric  cyanide,  in  water. 
The  hydrogen  of  hydric  cyanide  is  replaceable  by  simple 
or  compound  monad  radicles,  giving  rise  to  a  series  of 
compounds  termed  cyanides. 

495.  Potassic  Cyanide,  KCN.— This  compound  is  formed 
when   potassium    is   heated   in   cyanogen   gas,  or   hydric 
cyanide  vapor,  but  it  is  obtained  on  a  large  scale  by  the 
decomposition  of  potassic  ferrocyanide  (yellow  prussiate  of 
potash)   (K4FeC6N6),  by  heat.      It  is   a  \\hite  crystalline 
body,  very  soluble  in  water,  and  exceedingly  poisonous. 
It  is  much  used  in  the  arts  in  electroplating  and  gilding, 
and  in  the  laboratory  as  u  reagent. 

§  2.    Combustion. 

496.  Combustion  a  Chemical  Process.  — Combustion,  in 
its  popular  sense,  is  that  form  of  chemical  action  which  is 
accompanied  by  the  disengagement  of  heat  and  light,  and 
which  usually  takes  place  between  the  oxygen  of  the  air 
and  certain  organic  bodies,  as  wood,  coal,  oil.  etc.     The 
chemist,  however,  gives    to  the  term   a  wider  meaning, 
which  includes  all  those  forms  of  chemical  action  which 
result  in  the  combination  of  bodies,  with  one  or  all  of  the 
constituents  of  a  surrounding  gaseous  atmosphere;   thus 
the  violent  burning  of  iron  in  oxygen,  or  its  slow  rusting  in 
the  air,  the  rapid  consumption  of  wood  in  the  furnace,  or  its 
gradual  decay,  are  all  alike,  to  him,  cases  of  combustion. 
The   nature    of  the    gaseous   atmosphere    also   makes  .no 
difference,  and  phosphorus  or  arsenic  burning  in  chlorine 
gas,  hydrogen,  or  iron  in  sulphur-vapor,  are  instances  of 


£80  DESCRIPTIVE  CHEMISTRY. 

this  form  of  chemical  action,  as  well  as  the  corresponding 
changes  taking  place  in  air,  or  oxygen  gas.  Bodies  were 
formerly  divided  into  combustibles  and  supporters  of  com- 
bustion. Oxygen  was  held  to  be  the  universal  supporter 
of  combustion,  while  hydrogen,  carbon,  and  iron,  which 
burn  in  it,  were  called  combustibles.  But  if  the  atmos- 
phere were  hydrogen,  the  so-called  supporters  of  combustion 
would  burn  in  it  equally  well,  and  the  fact  is,  the  action  is 
mutual  and  of  the  same  kind  on  the  part  of  both. 

497,  Rapid  Combustion. — The  beginning  of  rapid  com- 
bustion is  termed  ignition.     In  order  to  induce  ignition 
a  certain  elevation  of  temperature  is  required,  and  the 
maintenance  of  this  temperature  is  essential  to  the  con- 
tinuance of  the  combustion.     After  a  substance  is  once 
kindled,  the  heat  given  off  by  the  rapid  chemical  action  is 
usually  more  than  sufficient  to  maintain  the  combustion 
until  the  burning  body  is  consumed.     The  temperature  at 
which  rapid  combustion  may  take  place   differs  with  dif- 
ferent bodies.    Thus,  in  atmospheric  air,  phosphorus  ignites 
at  150°  F.,  sulphur  at  480°  F.,  while  the  hydrocarbons  re- 
quire a  temperature   of  nearly  1000°  F.  to  kindle  them. 
The  stability  of  the  order  of  Nature  depends  upon  the  gra- 
dation of   the  affinities  between  atmospheric  oxygen  and 
the  hydrogen  and    carbon  of  organic  bodies.     These  are 
only  brought  into  action  at  high  temperatures.     Did  these 
bodies,  like  phosphorus,  ignite   at  a  much  lower  degree, 
conflagrations,  which  are  now  comparatively  rare,  would 
become  universal. 

498.  Explosive  Combustion. — When  two  gaseous  bodies, 
combustible  in  each  other,  are  mixed  and  ignited,  an  ex- 
plosion ensues.     This  is  because  the  constituents  of  the 
gaseous  mixture  are  so  intimately  blended  that  the  heat 
evolved  by  the  particles  first  ignited  passes  to  those  ad- 
joining, and   so  on  through  the   entire   mass,   with  such 
velocity  as  to    cause   an  almost  instantaneous  completion 
of  the   process.     The   products   pf   this  form    of  combus^ 


COMBUSTION.  281 

tion  are  always  in  the  form  of  highly-expanded  gases  or 
vapors,  the  intense  rarefaction  of  which  gives  rise  to  a 
vacuum,  and  the  particles  of  air  rushing  in  to  fill  thiy,  in 
colliding  with  each  other  produce  the  noise  of  the  explosion. 

499.  Slow  Combustion. — Oxygen,  as  well  as  other  ele- 
ments, frequently  enters  into  slow  combination  at  ordinary 
temperatures  and  without  perceptible  heat,  as  in  the  rust- 
ing of  iron  in  the  air.     The  cause  of  decay  in  vegetable 
and  animal  substances  is  the  slow  action  of  oxygen.     This 
slow  combustion  is  termed  eremacausis.     Heat,  however, 
always  accompanies   this  slow  form  of  combustion.     An 
ounce  of  iron  rusted  in  air,  or  burnt  in  oxygen,  produces 
the  same  amount  of  heat,  but  in  the  former  case  it  requires 
years  for  its  development,  and  in  the  latter  only  as  many 
minutes.     Sometimes,  under  favorable  circumstances,  the 
combination  becomes  so  rapid  that  the  accumulated  heat 
produces  ignition,  causing  the  phenomenon  called  spon- 
taneous combustion.      This  is  most  liable  to  occur  with 
porous  substances  which  expose  a  large  surface  to  the  air. 
The  tow  or  cotton  used  for  wiping  the  oil  from  machinery, 
and  then  laid  away  in  heaps,  often  ignites  in  this  manner, 
especially  if  exposed  to  the  sun. 

500.  Heat  of  Combustion. — The  complete  burning  of  a 
combustible  body  requires  the  consumption  of  the  same 
quantity  of  oxygen,  whether  the  process  goes  on  rapidly  or 
slowly,  and,  in  either  case,  the  amount  of  heat  set  free  is 
the  same.      Therefore,  the  intensity  of  the  heat  depends 
upon   the  rapidity  of   the  combustion.      Heat  would  be 
liberated  from  the  burning  of  a  pound  of  coal  in  ten  minutes, 
six  times  as  fast  as  if  its  combustion  occupied  an  hour. 
The  burning  in  air  of  one  pound  of  wood-charcoal  will 
raise  from  the  freezing  to  the  boiling  point  73  Ibs.  of  water; 
one  pound  of  mineral  coal  will  correspondingly  heat  60  Ibs. 
of  water ;  and  one  pound  of  dry  wood  will  raise  35  Ibs.  of 
water  through  the  same  number  of  degrees.     These  are  the 
highest  results  by  careful  experiments ;  in  practice  we  pb- 


282  DESCRIPTIVE   CHEMISTRY. 

tain  a  much  lower  eff-.ct,  both  on  account  of  imperfect 
combustion,  and  from  the  fact  that  a  large  proportion  of 
the  heated  air  escapes  through  the  chimney,  before  it  has 
given  off  as  great  an  amount  of  heat  as  it  is  capable  of 
producing. 

501.  Cause  of  the  Heat. —  It  has   been  explained   that 
chemical  action  produces  heat  by  conversion  of  the  motion 
of  chemical  atoms  into  heat-vibrations.     We  have  atoms 
separated  and   powerfully  attracted,  like  lifted   weights ; 
they  rush  together,  collision  arrests  motion,  and  their  force 
is  given  out  as  heat.     It  is  the  clash  or  impact  of  the  atoms 
of  oxygen  against  the  elements  of  burning  bodies,  which 
gives  us  the  heat  and  light  of  combustion.     By  figuring 
to  ourselves   the  atoms  shot  across  the  molecular  spaces 
with  intense  force,  and  thus  parting  with  their  motion,  we 
have  an  explanation  of  the  source  of  heat  in  combustion, 
which    is  in  harmony  with  our   latest   knowledge  of   the 
nature  of  heat,  and  of  its  other  modes  of  production,  while 
in  no  other  way  is  it  possible  to  explain  its  chemical  origin. 

502.  Nature  of  Flame. — Flame  is  produced  by  the  com- 
bustion of  gas?s.     Substances  which  burn  with  flame  are 
either  gases  already,  or  they  contain  a  gas  which  is  set 
free  by  the  heat  of  combustion.     But  flame  does  not  ne- 
cessarily produce  light.     In  the  burning  of  pure  oxygen 
and  hydrogen,  there  is  intense  flame,  but  so  little  light  that 
it  can  hardly  be  seen.     ]f,  into  this  non-luminous  flame,  we 
sift  a  little  charcoal-dust,  the  particles  of  solid  carbon  are 
instantly  heated  to  incandescence,  and  there  is  a  bright 

flash  of  liffht.     The  conditions  of 

.PIG.   loo. 

illumination  are,  therefore,  first,  an 
intense  heat ;  and,  second,  a  solid 
placed  in  the  midst  of  it,  which 
remains  fixed,  a,nd  gives  out  the 
light. 

503,  The  Compound  Blow-pipe, 
-pipe,         —These    conditions    are    fulfilled 


COMBUSTION. 

most  perfectly  by  means  of  the  compound  blow-pipe  of  Dr. 
Hare.     The  two  gases  are  collected  in  gasometers,  or  India- 
rubber  bags,  Fig.  183,  which  are  connected  by  flexible  tubes 
with  the  brass  jet.  Fig.  184 ;  the 
flow  being  increased  by  pressure 
on  the  bags,  and  controlled  by 
stop-cocks.    The  gases  are  emit- 
ted together  and  burned  at  the 
orifice,  a.     When  ignited,  they 
give  rise  to  a  blue  flame  which 
is  hardly  visible,  but  which  has  Blow-pipe  Jet. 

intense  heating  power,  and  pro- 
duces the  most  remarkable  effects.     A  steel  watch-spring 
burns  in  it  with  a  shower  of  scintillations.      Substances 
which   do  not  fuse   in    the  hottest  blast-furnaces  melt  in 
this  heat  like  wax,  or  dissipate  in  vapor. 

504.  The  Lime-BalL — A  little  ball  of  lime,  however,  of 
the  size  of  a  pea,  remains  unaltered  in  the  flame.     It  glows 
with  a  blinding  brilliancy,  producing  what  is  known  as  the 
"  Drummond  light,"  or  the  "  calcium  light."      It  is  em- 
ployed as  a  substitute  for  the  rays  of  the  sun  in  the  solar, 
or  oxyhydrogen  microscope,  and  is  used  in  coast-surveys 
for  night-signals.     In  all  ordinary  illuminations  the  prin- 
ciple is  the  same  as  that  of  the  lime-light.     The  substances 
employed  are  compounds   of  carbon   and  hydrogen;    the 
union  of  oxygen  and  hydrogen  gives  rise  to  heat,  and  the 
luminous  carbon-particles  at  the  same  time  set  free  in  the 
heated  space  are  the  source  of  the  light. 

505.  How  the  Candle  burns. — The  materials  used  for 
illumination,   whether   solids  or  liquids,    are   always   con- 
verted into  gas  before  burning.     The  candle  first  becomes 
a  lamp,  and  then  a  gas-burner.     "When  lighted,  the  heat 
radiates  downward,  so  as  to  melt  the  material  of  the  can- 
dle and  form  a  hollow  cup  filled  with  the  liquid  combus- 
tible, Fig.  185,  and  thus  the  candle  becomes  an  oil-burner. 
From  this  reservoir,  the  wick  draws  up  the  oil  into  the 


284 


DESCRIPTIVE   CHEMISTRY. 


FIG.  185. 


Burning 
Candle. 


flame.  Here,  in  the  midst  of  a  high  heat,  and  cut  off  from 
the  air,  it  undergoes  another  change  exactly  as  if  it  were 
inclosed  and  heated  in  a  gas-maker's  retort ;  it 
is  converted  into  gas,  and  in  this  form  finally 
burned.  As  the  wick  rises  into  the  flame,  it 
fills  the  interior  with  a  sooty  mass,  and  inter- 
feres with  the  combustion. 

506.  Structure  of  the  Flame,— As  the  wick 
remains  thus  unconsumed  in  the  interior  of 
tha  flame,  it  is  obvious  there  can  be  no  fire 
there.  If  we  lower  a  piece  of  glass  or  a  wire 
gauze  over  a  candle  or  gas  flame,  as  in  Fig.  186, 
we  shall  see  an  interior  dark  space  surround- 
ed by  a  ring  of  fire.  This  inner  sphere  is  filled 
with  dark  unburned  hydrocarbon  vapors,  which 
are  inclosed  by  a  shell  of  fire,  or  burning  gas. 
If  one  end  of  a  small  glass  tube  be  introduced  into  the 
candle-flame,  as  in  Fig.  187,  these  in- 
terior gases  will  be  conveyed  away, 
and  may  be  lighted  at  the  other  end. 

507.  Order  of  the  Combustion. — 
There  is  an  order  of  combustion  in 
the  flame,  which  depends  upon  the  or- 
der of  affinities.  In  Fig.  188,  a  repre- 
sents the  nucleus  of  hydrocarbon  va- 
por. If,  now,  oxygen  from  without 
had  the  same  affinity  for  both  its  ele- 
ments, they  would  be  consumed  to- 
gether, with  but  little  luminous  effect. 
But  the  oxygen  decomposes  the  gas- 
eous compound,  and,  seizing  upon 
the  hydrogen  first,  surrounds  a  with 
the  intensely  heated  space,  b.  At  the 
same  time  the  carbon-particles  are  set 
free,  and,  being  heated  white-hot,  give 

Out  the    motion    of  light.      The  COne  b  Gas  from  Flame. 


FIG.  186. 


The  Flame  hollow. 
FIG.  1ST. 


COMBUSTION. 


285 


FIG.  188. 


FIG.  189. 


is  therefore  the  place  of  burning  hydrogen  and  the  seat  of 
illumination.  The  incandescent  carbon-particles,  as  they 
pass  outward,  meet  with  oxygen  at  c,  and  are 
converted  into  carbonic  dioxide  in  the  outer  cone. 
To  prove  the  constant  presence  of  free  carbon  in 
the  flame,  it  is  only  necessary  to  introduce  into 
it  any  cold  body,  as  a  piece  of  porcelain,  when 
carbon  will  be  copiously  deposited  upon  it  as 
soot.  Fig.  189  represents  a  cross-section  of  the 
flame  and  the  arrangement  of  its  parts ;  CH  the 
unburned  carbon  and  hydrogen,  H  the  sphere  of 
burning  hydrogen  across  which  the  carbon-parti- 
cles float,  and  lastly  the  sphere  of  burning  car- 
bon. It  will  be  observed,  by  noting  any  com- 
mon flame,  that  at  the  base  it  burns  blue,  and 

yields  but  little  light.  This  is  because  the 
oxygen  at  this  point  is  so  abundant  that 
it  burns  simultaneously  both  hydrogen 
and  carbon.  A  candle-flame  moved  swift- 
ly through  the  air  gives  a  diminished  light 
for  the  same  reason. 

508.  Effect  of  Temperature  on  the 
Flame. — The  amount  of  light  produced 
depends  upon  the  intensity  of  the  heat. 
Dr.  Draper  found  that  a  body  at  2,600°  emitted  almost  40 
times  as  much  light  as  at  1,900°.  If 
by  any  means  the  temperature  of  the 
flame  falls  below  a  certain  limit  it  is  im- 
mediately extinguished.  The  flame  of  a 
candle  may  be  put  out  by  lowering  over 
it  a  coil  of  cold  copper  wire,  Fig.  190.  A  piece  of  fine 
wire  gauze  held  across  the  flame  of  a  candle  cools  the  com- 
bustible gases  below  the  point  of  ignition,  so  that  they 
rise  through  the  meshes  in  the  form  of  smoke,  Fig.  191. 
The  gauze  may  become  red-hot  and  still  not  allow  the  flame 
to  pass,  so  rapidly  is  the  heat  conducted  away  by  the  wire. 


Cross-Section  of  the 
Flame. 


FIG.  190. 


Copper  CoiL 


286 


DESCRIPTIVE   CHEMISTRY. 


FIG.  191. 


Gauze  stops  the  Flame 


Yet  the  cooled  gases  may  be  rekindled  above,  when  the 
flame  will  go  on  burning  as  before,  Fig.  192. 

509,  Safety -Lamp.— On  this  principle  the  safety-lamp  is 

constructed.    The  explosions 
of    hydric   carbide   in    coal- 
mines caused    immense   de 
struction  of  life,  and  various 
arrangements  had  been  fruit- 
lessly contrived  to  prevent 
these  terrible  accidents  when 
Sir  Humphry  Davy  took  hold 
of   the   subject.       He   com- 
menced a  series  of  research- 
es  upon    flame    in    August, 
1815,  and  with  such  success 
as  to  produce  the  perfected 
lamp  at  the  Royal  Institution  of  London  in  the  succeeding 
November.     The  safety-lamp  consists  simply  of  an  ordi- 
nary oil-lamp  inclosed  in  a  cage  of  wire 
gauze  which  permits  the  light 
to  pass,  out,  but  prevents  all 
exit  of  flame,  Fig.  193.     The 
space  within  the  gauze  often 
becomes    filled    with    flame, 
from     the    burning    of     the 
mixed  gases  which  penetrate 
the  net-work;  but  the  isola- 
tion is  so  complete  that  the 
explosive  mixture  without  is  not  fired.     Fatal 
explosions   still    occasionally   take    place,    but 
they  are  due  to   carelessness   of    the  miners. 
As  the   intensity  of  light  depends   upon   the 
rapid  consumption  of  oxygen,  there  must  be  a 
free  supply  of  air,  and  provision  for  the  escape 
Safety -Lamp    of  combustion  products. 


FIG.  192. 


FIG.  193. 


Ga.»  hums  above. 


HYDROCARBONS  AND   THEIR   DERIVATIVES.         287 


DIVISION   III.-ORGANIC   CHEMISTRY. 


CHAPTER   XXV. 

§  1.  Hydrocarbons  and  their  Derivatives. 

510.  The  Marsh-Gas  Series  (Paraffins). — When  the  unit- 
weight  of  carbon  combines  with  four  unit-weights  of  hy- 
drogen the  result  is  the  simplest  known  hydride  of  car- 
bon, and  since  this  is  a  saturated  compound,  or  molecule, 
it  is  incapable  of  combining  with  chlorine,  bromine,  or 
any  monad  element,  but  it  may  exchange  the  whole  or  a 

Fir.    194. 


March-Gas. 


part  of  its  hydrogen  for  an  equivalent  quantity  of  another 
element.      It  is  from  these  hydrocarbons,  or  compounds 
having  this  composition,  that   more   or  less  directly  the 
13 


288  DESCRIPTIVE    CHEMISTRY. 

organic  substances,  to  be  hereafter  described,  may  be 
built  up. 

Methane,  CH4  (Marsh-Gas)^  is  the  first  member  of  a 
series,  each  term  of  which  differs  from  the  term  next  below 
by  CH,. 

It  is  a  colorless,  inodorous,  tasteless,  inflammable  gas, 
which  burns  with  a  yellow,  luminous  flame.  If  diluted 
with  air,  it  is  not  injurious  to  life.  It  may  be  produced  by 
heating  in  a  glass  flask  a  mixture  of  two  parts  of  sodic 
acetate,  three  parts  of  potassic  hydrate,  and  three  of  quick- 
lime. It  is  called  marsh-gas  because  it  is  a  product  of  the 
decomposition  of  vegetable  matter  contained  in  the  mud  of 
stagnant  pools.  It  may  be  collected  by  inverting  a  jar  and 
funnel  in  the  water,  and  stirring  the  mud  beneath,  Fig.  194, 
when  the  gas  rises  into  the  jar  in  bubbles.  It  is  often  dis- 
engaged in  large  quantities  in  coal-mines :  mixed  with  the 
air  it  becomes  explosive,  and  constitutes  the  fatal  fire- 
damp. If  the  air  is  more  than  six  times  or  less  than  four- 
teen times  the  bulk  of  the  gas,  the  mixture  explodes  vio- 
lently. Carbonic  dioxide  is  produced  by  the  combustion,  so 
that  those  who  are  not  killed  by  the  burning  or  shock  are 
generally  suffocated  by  the  choke-damp. 

In  some  places,  this  gas  rises  from  the  earth  in  such 
quantities  as  to  be  utilized  for  purposes  of  illumination ;  as 
in  the  village  of  Fredonia,  N.  Y.  In  the  deep  wells  sunk 
for  brine  and  mineral  oil,  it  often  rises  in  such  quantity  as 
to  be  employed  for  driving  the  pumping-engines,  or  for 
evaporating  the  liquids. 

Petroleum  (Rock- Oil)  is  a  natural  product  found  on 
this  continent,  in  Canada,  and  in  Pennsylvania.  In  some 
cases  it  rises  to  the  surface  of  the  earth,  but  more  general- 
ly it  is  obtained  by  sinking  wells  into  the  strata  in  which 
it  occurs.  It  is  a  thick,  greenish,  oily  liquid,  of  variable 
composition. 

511.  Coal-Oil  consists,  to  a  great  extent,  of  a  mixture 
of  various  compounds  of  the  Paraffin  Series.  It  is  a  prod- 


HYDROCARBONS  AND  THEIR  DERIVATIVES.         289 

uct  of  the  distillation  of  bituminous  coal,  bituminous 
shales,  and  asphalt.  The  material  is  placed  in  iron  retorts, 
in  large  pits  holding  a  hundred  tons,  or  in  kilns  of  brick 
containing  twenty-five  tons.  The  retorts  are  heated  from 
without,  like  gas-retorts,  while  the  kilns  are  fired  within, 
like  the  tar-pits.  The  first  product  collected  in  the  reser- 
voirs resembles  the  natural  oil  from  the  wells,  and  is  re- 
fined by  the  same  method.  It  is  first  distilled  at  a  tem- 
perature of  600°  or  800°  F.,  and  the  product,  conveyed  to 
cisterns  holding  3,000  gallons,  is  agitated  with  5  or  6  per 
cent,  of  hydric  sulphate.  The  acid  and  settled  impurities 
being  drawn  off  at  the  bottom,  the  mass  is  again  agitated, 
first  with  water,  and  afterward  with  alkaline  lye ;  it  is  then 
redistilled,  and  constitutes  the  "  kerosene  "  or  "petroleum- 
oil"  of  commerce.  It  has  been  found  by  experience  that 
it  is  not  safe  to  use  a  paraffin-oil  which  will  take  fire  on 
the  application  of  a  match,  and  burn  continuously  at  a 
temperature  below  100°  F.  The  reason  for  this  may  be 
found  in  the  fact  that  the  oils  obtained  by  the  distillation 
of  coal,  at  low  temperatures,  are  mixtures  of  paraffins,  dif- 
fering in  volatility,  and  unless  the  volatile  members  of  the 
series  have  been  driven  off  by  proper  distillation,  the  oils 
take  fire  easily,  give  off  inflammable  vapors  which,  mixing 
with  air  in  the  body  of  the  lamp,  form  compounds  which 
are  dangerously  explosive. 

Paraffin  is  a  crystalline,  colorless,  inodorous,  tasteless, 
and  fatty  substance,  probably  a  mixture  of  several  of  the 
higher  terms  of  this  series.  It  is  found  native  in  coal-beds 
and  other  bituminous  strata,  as  fossil  wax,  mineral  tallow, 
etc.  It  may  also  be  procured  from  petroleum  and  from 
coal-oil.  As  it  burns  with  a  bright  flame  and  is  hard,  it 
makes  excellent  candles.  It  is  used  as  a  substitute  for  sul- 
phur in  dipping  matches,  and  to  render  woolen  cloths 
stronger  and  water-proof. 

512,  Olefine  Series  of  Hydrocarbons. — This  series  in- 
cludes a  number  of  interesting  bodies.  The  lowest  terms 


290  DESCRIPTIVE   CHEMISTRY. 

of  the  series  are  gaseous  at  ordinary  temperatures;  the 
highest  solid,  and  the  intermediate  compounds  liquid. 

Ethylene^  C3H4  (Olefiant  Gas). — This  gas  may  be  pre- 
pared by  mixing  strong  alcohol  with  five  or  six  times  its 
weight  of  sulphuric  acid  in  a  retort,  and  applying  heat.  It 
is  colorless,  tasteless,  nearly  as  heavy  as  air,  with  a  marked 
odor,  very  inflammable,  and  burns  with  a  bright  and  in- 
tensely luminous  flame.  When  mixed  with  air  it  is  explo- 
sive, and  derives  its  name  (oil-former)  from  the  fact  that  it 
forms  an  oily  compound  with  chlorine.  It  was  liquefied 
under  great  pressure  by  Faraday.  It  is  decomposed  by 
electric  sparks  into  carbon  and  methane. 

Illuminating  gas  consists  of  a  mixture  of  various  gases 
— hydrogen,  methane,  nitrogen,  ethylene,  carbonic  monox- 
ide and  dioxide,  and  hydric  sulphide  being  represented  in 
the  largest  quantities.  The  illuminating  power  of  the 
gas  is  nearly  proportional  to  the  quantity  of  ethylene 
which  it  contains.  It  is  commonly  produced  from  bitu- 
minous coal,  placed  in  cast-iron  retorts,  fixed  in  furnaces, 
and  heated  to  redness  by  an  external  fire.  Each  retort 
receives  a  charge  of  100  to  150  Ibs.  of  coal  every  six 
hours,  and  in  large  gas-works  several  hundreds  of  them  are 
kept  at  work  day  and  night.  At  a  moderate  heat,  tar  and 
oil  are  produced,  but,  at  a  high  temperature,  gases  are 
formed  in  large  quantities.  Besides  the  products  of  this 
destructive  distillation  above  mentioned,  there  are  present 
a  thick,  black  liquid,  known  as  coal-tar,  steam,  various  arn- 
moniacal  compounds  and  a  solid,  friable,  carbonaceous  mass 
known  as  coke. 

Illuminating  gas  has  come  into  use  entirely  within  the 
present  century,  it  having  been  first  employed  in  London 
in  1802.  How  wonderful  that  sunbeams  absorbed  by  vege- 
tation in  the  primordial  ages  of  the  earth,  and  buried  in  its 
depths  as  vegetable  fossils  through  immeasurable  eras  of 
time,  until  system  upon  system  of  slowly-formed  rocks 
have  been  piled  above,  should  come  forth  at  last,  at  the 


\ 
HYDROCARBONS  AND   THEIR    DERIVATIVES.          291 

disenchanting  touch  of  Science,  and  turn  the  night  of  civil- 
ized man  into  day ! 

513.  Acetylene,  C2H,. — This   compound   is   of   special 
interest  as  a  hydrocarbon  which  can  be  obtained  by  the 
direct    union   of   its   elements.      It    is    formed   when    the 
current  from  a  powerful  battery  passes,  in  an  atmosphere 
of  hydrogen,  between  carbon-poles.     It  is  also  the  product 
of  decomposition  by  heat  or  imperfect  combustion  of  or- 
ganic compounds. 

514.  Turpentine  Series. — This   series  is  interesting  as 
including  an   isomeric  group  of  the   composition   C10H16, 
called   Terpenes,  which  occur,  widely  distributed  through 
the  vegetable  kingdom,  as  the  essential  oils,  to  the  pret- 
ence of  which  the  peculiar  odor  of  certain  plants  is  due. 

Terpenes,  C10H16. — The  volatile  oil  of  turpentine,  also 
known  as  "  spirits  of  turpentine,"  may  be  taken  as  a  type 
of  this  class  of  substances.  It  is  obtained  by  distilling  with 
water  the  pitchy  matter  that  exudes  from  various  species 
of  pine  and  other  trees.  Oil  of  turpentine  is  a  colorless, 
limpid  fluid,  having  a  strong  odor  and  disagreeable  taste. 
It  boils  at  320°  F.,  and  has  a  specific  gravity  of  0'86.  It  is 
highly  inflammable,  and  when  purified  is  used  for  illumi- 
nating purposes,  under  the  name  of  camphene.  Burning 
fluid  is  rectified  turpentine  or  camphene,  dissolved  in  alco- 
hol, which  admixture  renders  it  less  smoky  when  burned. 
Spirits  of  turpentine  is  also  used  in  varnishes  as  a  solvent 
for  resins  and  gums.  The  oils  of  lemon  and  orange  are  also 
terpenes. 

515.  Benzine  Series. — The   hydrocarbons  of  this  class 
are  found  in  coal-tar  and  in  the  petroleum  which   is  ob- 
tained from  Rangoon,  in  the  kingdom  of  Burmah.    Benzol, 
or  benzene  (C6He),  is  very  much  used  in  the  arts.     It  is  a 
colorless,  volatile  liquid,  the  vapor  of  which  is  very  inflam- 
mable.    It  burns  with  a  smoky  flame.     Benzol  is  valuable 
as  a  solvent,  readily  dissolving  phosphorus,  sulphur,  and 
caoutchouc,  as  well  as  wax  and  all  fatty  bodies. 


292  DESCRIPTIVE   CHEMISTRY. 

By  the  action  of  nitric  acid  on  benzene,  a  heavy  oily 
liquid  called  nitro-benzene  is  produced.  It  has  an  odor  re- 
sembling that  of  bitter  almonds,  and  is  used  in  perfumery, 
but  it  is  chiefly  interesting  as  being  a  stepping-stone  in  the 
production  of  aniline,  C6H7N,  which  has  of  late  years  ac- 
quired special  importance  as  the  basis  of  the  well-known 
aniline  colors.  Aniline  is  obtained  indirectly  from  benzene, 
one  of  the  chief  constituents  of  coal-tar,  though  it  also 
occurs  in  the  coal-tar,  ready  formed,  in  small  quantities. 
It  is  a  colorless,  mobile,  oily  liquid  of  faint,  agreeable, 
vinous  odor,  and  aromatic,  burning  taste.  It  boils  at  182° 
C.,  solidifies  at  very  IOAV  temperatures,  is  easily  soluble  in 
alcohol  and  ether,  and  slightly  soluble  in  water.  It  is 
poisonous. 

Naphthalene,  C10II8,  closely  resembles  benzene  in  chem- 
ical reactions.  It  is  a  product  of  the  decomposition  of 
many  hydrocarbons  by  a  red  heat,  and  is  obtained  abun- 
dantly in  the  distillation  of  coal-tar.  It  is  solid  at  ordi- 
nary temperatures,  insoluble  in  water,  but  dissolves  in  al- 
cohol. 

Anthracene,  C14H10,  is  a  white  solid,  and  is  one  of 
the  last  products  of  the  distillation  of  coal-tar.  It  has 
lately  attracted  much  attention  owing  to  the  fact  that 
alizarine,  the  red  coloring  substance  of  the  madder-roots, 
has  been  obtained  from  it.  Carminic  acid — the  coloring- 
matter  of  cochineal — is  used  for  dyeing  wool  and  silk 
crimson  or  scarlet,  but  the  colors,  though  brilliant,  are  not 
durable, 

§  2.  Alcohols. 

516.  The  term  alcohol,  which  originally  designated  only 
one  substance,  viz,,  spirit  of  wine,  has  now  a  much  wider 
meaning,  and  is  applied  to  quite  a  large  number  of  com- 
pounds, many  of  which  in  their  external  characteristics 
exhibit  but  little  likeness  to  common  alcohol.  They  are 
all  compounds  of  oxygen,  hydrogen,  and  carbon,  and  may 


ALCOHOLS.  293 

be  regarded  as  derived  from  the  hydrocarbons  of  the  rnarsh- 
gas  series  by  substituting  for  a  single  atom  of  hydrogen 
the  radicle  hydroxyl  (HO),  as,  for  example,  common  al- 
cohol. 

H    H    ! 


H-C-C- 
A   A 


-0-H 


Methyl  Alcohol,  CH4O  (  Wood- Spirit).— This  is  one  of 
the  chief  products  of  the  dry  distillation  of  wood.  When 
pure  it  is  a  thin,  colorless  liquid,  very  similar  in  smell  and 
taste  to  common  alcohol.  Crude  wood-spirit,  however,  is 
always  impure,  has  an  offensive  odor,  and  a  nauseous,  burn 
ing  taste.  It  is  employed  in  the  arts  for  many  of  the  pur- 
poses for  which  ordinary  alcohol  is  used,  especially  in  the 
manufacture  of  varnishes. 

517.  Ethyl  Alcohol,  CaH6O  (Common  Alcohol,  Spirits 
of  Wine). — When  solutions  of  sugar  (CiaHMOn),  or  the 
sweet  saccharine  juices  of  plants,  are  acted  upon  by  fer- 
ments, they  are  decomposed,  with  evolution  of  carbonic 
dioxide,  and  formation  of  alcohol.  This  substance  may 
also  be  obtained  from  ethylene ;  ethylene  may  be  prepared 
from  acetylene  (513),  and  thus  it  will  be  seen  that  it  is 
possible  by  a  series  of  simple  reactions  to  build  up  alcohol 
from  the  elements  carbon,  oxygen,  and  hydrogen.  It  is  a 
colorless,  mobile  fluid,  of  0.77  specific  gravity,  having  a 
pleasant,  fruity  smell,  and  a  burning  taste.  It  is  very  vola- 
tile, and  has  a  strong  tendency  to  absorb  moisture  from  the 
air  or  from  bodies  immersed  in  it,  thus  rendering  it  valu^ 
able  as  an  antiseptic.  It  is  highly  combustible,  burning 
with  a  pale-blue  flame,  and  producing  intense  heat  without 
smoke ;  it  is  therefore  well  adapted  to  burn  in  lamps  for 
chemical  use.  Alcohol  has  great  value  as  a  solvent,  as  it 
acts  upon  many  substances  which  water  does  not  dissolve, 
and  is  easily  separated  from  them  on  account  of  its  extreme 
volatility.  It  boils  at  173°  F.,  and  has  never  been  frozen, 


294  DESCRIPTIVE   CHEMISTRY. 

although  at  — 166°  it  becomes  viscid.  In  a  concentrated 
form  it  is  a  potent  poison,  but,  when  sufficiently  diluted,  it 
acts  upon  the  animal  system  as  a  stimulant.  Taken  freely 
in  this  form  it  produces  inebriation,  and  is  the  active  prin- 
ciple of  all  intoxicating  liquors. 

518.  Amyl  Alcohol,  C6H12O  (Fusel  Oil).— This  alcohol 
is  produced  together  with  ordinary  alcohol  in  fermentation. 
It  is  a  transparent,  colorless  liquid,  of  unpleasant,  mouldy, 
spirituous  odor,  and  burning  taste,  and  is  poisonous.     It 
burns  with  a  white,  smoky  flame,  and  has  been  used  for 
illuminating  purposes. 

519.  Wines  are  obtained  from  the  expressed  juice  of 
the  grape  and  other  fruits.    The  fresh  grape-juice,  or  must, 
is  placed  in  vats  in  cellars,  where  the  temperature  is  so 
low  that  the  fermentation  proceeds  very  slowly.     Some- 
times the  wines  are  bottled  before  the   fermentation   is 
quite  complete,  and  they   continue   to  generate  carbonic 
dioxide,  which  remains  compressed  within  the  liquid.     If 
the  carbonic  dioxide  is  so  abundant  as  to  produce  efferves- 
cence when  uncorked,  the  wine  is  said  to  be  "  sparkling  • " 
if  otherwise,  it  is  termed  "still"  wine. 

520.  Lager-Beer  is  freed  from  nitrogenized  products  by 
a  slow  and  long-continued  fermentation ;  hence  it  may  be 
preserved  for  years  without  further  decomposition.    Before 
consumption  it  lies  stored  in  vaults  for  months,  from  which 
circumstance  its  name  is  derived  (lager,  lair).     The  differ- 
ence in  color  of  malt  liquors  is  owing  to  the  various  degrees 
of  heat  employed  in  malting.     Ale  is  made  from  pale  malt, 
while  that  used  for  porter  is  partially  charred,  giving  it  a 
brownish  color  and  bitter  flavor. 

521.  Distilled  Liquors  are  obtained  by  subjecting  cer- 
tain fermented  mixtures  to  distillation.    Brandy  is  derived 
from  the  distillation  of  wine ;  rum  from  that  of  fermented 
molasses,  and  arrack  from  the  distillation  of  fermented  rice- 
infusion.    Whiskey  is  obtained  from  corn,  rye,  and  potatoes, 
by  first  converting  their  starch  into  sugar,  then  into  spirit, 


ALCOHOLS.  295 

and  distilling  the  product.  Grin  is  produced  from  the  dis- 
tillation of  the  spirit  of  a  mixture  of  barlev  and  rye,  and 
owes  its  peculiar  flavor  to  juniper-berries. 

522.  Phenol,  CeH8O.— A  substance  familiarly  known  as 
carbolic  acid  is  regarded  by  the  chemist  as  the  alcohol  of 
benzene : 

Benzene,  C6He.     Phenol,  C6H6OH. 

The  chief  source  of  phenol  is  coal-tar,  from  which  it  is 
obtained  by  distillation.  Pure  phenol  crystallizes  at  or- 
dinary temperatures  in  long,  colorless,  needle-shaped  prisms, 
which  attract  moisture  from  the  air,  deliquescing  to  an  oily 
hydrate.  The  crystals  melt  at  35°  C.,  and  boil  at  180°  C., 
are  slightly  soluble  in  water,  more  freely  in  alcohol.  They 
have  a  penetrating,  smoky  odor  and  a  burning  acrid  taste. 
Phenol  and  its  solutions  have  in  an  eminent  degree  the 
property  of  preserving  animal  substances  from  decay,  and 
are  on  this  account  much  employed  as  antiseptics  and  dis- 
infectants. A  considerable  portion  of  the  creosote  of  com- 
merce consists  of  phenol.  Genuine  creosote  is  a  colorless, 
oily  liquid  with  a  smoky  odor  and  burning  taste.  It  is  a 
powerful  antiseptic,  and  meat,  steeped  for  a  few  hours  in 
a  solution  of  one  part  creosote  to  100  parts  water,  remains 
sweet  and  will  not  putrefy.  Creosote  is  used  very  exten- 
sively in  medicine,  both  inwardly  and  as  an  external  appli- 
cation, but  an  overdose  is  a  corrosive  poison.  Crude  pyro- 
ligneous  acid,  on  account  of  the  creosote  it  contains,  is 
used  to  preserve  meats,  to  which  it  imparts  a  smoky  flavor. 
The  curing  quality  of  the  smoke  of  green  wood  is  also 
owing  to  this  cause.  It  is  the  vapor  of  creosote  which 
renders  smoke  so  irritating  to  the  eyes. 

523.  Fats  and  Oils.— Most  of  the  fixed  oils,  and  the  fats, 
both  animal  and  vegetable,  are  compounds  of  glycerine, 
and  acids  of  the  acetic  and  oleic  type.     Thus  beef  and 
mutton   fat  consist  mainly  of  stearic  glyceride  (stearin) ; 
olive-oil  is  oleic  glyceride  (olein) ;  palm-oil  is  chiefly  pal- 


296  DESCRIPTIVE  CHEMIS:RY. 

mitic  glyceride  (palmitine).  These  glycerides,  when  de- 
composed, by  heating  with  water  yield  glycerine  and  an 
acid. 

Glycerine  (CgH8O3). — When  pure  this  substance  is  a 
nearly  colorless,  inodorous,  sirupy  liquid,  of  intensely  sweet 
taste.  It  is  readily  soluble  in  water  and  alcohol,  and  is  a 
powerful  solvent  and  antiseptic.  Of  late  years,  it  has  been 
employed  as  a  medicine ;  and,  on  account  of  its  solvent 
power,  it  is  also  largely  used  as  a  vehicle  for  administering 
other  medicines.  It  is  extensively  employed  in  the  manu- 
facture of  cosmetics  and  perfumery.  Glycerine  is  non- 
volatile, and,  when  heated  over  600°  F.,  is  decomposed, 
giving  off  among  other  products  a  peculiar  acrid  substance 
termed  acroleine  (C3H4O).  This  is  the  body  which  causes 
the  irritating  fumes  of  a  smouldering  candle-wick  and  of 
burning  fats  when  the  combustion  is  in  complete. 

524.  Nitro-glycerine,  CSHB(NO3)3.— When  a  mixture 
of  strong  sulphuric  and  nitric  acids  acts  on  glycerine,  at  low 
temperatures,  a  violently  explosive,  oily  liquid  of  light- 
yellow  color  is  produced.  This  compound  has  a  specific 
gravity  at  15°  C.  of  1.6,  is  inodorous,  but  has  a  sweet, 
pungent,  aromatic  taste,  and,  placed  upon  the  tongue,  pro- 
duces headache.  Nitro-glycerine  is  exploded  not  by  the 
direct  application  of  heat,  but  by  sudden  concussion,  and 
proper  care  in  its  preparation  greatly  lessens  the  danger 
accompanying  its  use. 

§  3.  Saccharine  Bodies. 

525. — Saccharine  bodies,  sometimes  called  carbo-hy- 
drates, constitute  an  important  class  of  substances,  inter- 
esting on  account  of  their  wide  distribution  in  the  vege- 
table world.  Among  these  substances  we  have  the  sugars 
proper,  grape-sugar,  gum,  starch,  and  woody  fibre.  These 
are  probably  related  to  the  alcohols,  though  their  exact 
composition  has  not  in  all  cases  been  ascertained.  Two 


SACCHARINE   BODIES.  297 

of  these  compounds,  grape  and  fruit  sugar,  break  up  into 
alcohol  and  carbonic  dioxide  under  the  influence  of  yeast. 
Dextrose,  or  grape-sugar,  C6H12Oe,  is  widely  distributed 
in  all  ripe  fruits,  and  may  be  prepared  by  boiling  starch  in 
dilute  sulphuric  acid.  Isomeric  with  this  compound  is 
Icevulose,  or  fruit-sugar,  which  occurs  mixed  with  other 
varieties  of  sugar  in  the  juices  of  ripe  fruit,  honey,  etc. 
Both  of  these  compounds  belong  to  the  group  of  glucoses. 

526.  Cane-Sugar,  CiaHMOn,  is  produced   chiefly  from 
the    cane,  beet-root,  sorghum,  and   the    palm  and   maple 
trees;  but  by  far  the  largest  portion   is  from  the  sugar- 
cane.    The  canes  are  crushed  by  passing  them  between 
grooved  iron  cylinders.     The  juice,  when  first  expressed, 
is  liable  to  rapid  decomposition  from  the  heat  of  the  cli- 
mate.    This  is  prevented  by  the  addition  of  a  small  quan- 
tity of  lime,  which  neutralizes  acids  and  coagulates  impu- 
rities.    The  juice  is  evaporated  by  boiling  in  large,  open 
vessels,  and,  when  reduced  to  a  proper  consistency,  is  trans- 
ferred to  coolers,  where  a  portion  of  it  crystallizes,  forming 
raw  or  brown  sugar.     On  an  average,  a  gallon  of  juice 
produces  a  pound  of  sugar. 

Crude  sugars  are  purified,  or  refined,  by  reducing  them 
to  a  sirup,  which  is  first  filtered  through  twilled  cotton,  to 
separate  mechanical  impurities.  The  same  effect  is  further 
promoted  by  the  use  of  serum  of  blood.  To  decolorize  the 
sirup  it  is  again  filtered  through  a  bed  of  coarsely-pow- 
dered bone-black  or  animal  charcoal.  It  is  then  evaporated 
in  vacuum-pans — the  air  being  exhausted,  so  that  it  will 
boil  at  a  lower  temperature — and  finally  recrystallized. 
The  drainage  of  the  raw  sugar  forms  molasses. 

527.  Properties. — Pure  cane-sugar  has  a  specific  gravity 
of  1.6,  is  soluble  in  about  one-third  of  its  weight  of  cold 
water,  forming  a  thick  sirup,  and  separates  from  concen- 
trated solutions   in   large,  transparent,  colorless  crystals, 
having  the  shape  of  oblique  rhombic  prisms  or  modified 
forms.     It  melts  at  about  320°C.,  and  solidifies,  on  cooling, 


298  DESCRIPTIVE   CHEMISTRY. 

to  a  transparent,  amber-colored  substance,  known  as  bar- 
ley-sugar. If  the  melted  sugar  be  heated  to  420°C.,  it 
changes  to  a  dark-brown  mixture  of  several  different  bodies, 
which  is  termed  caramel,  and  is  much  used  for  coloring 
sirups  and  liquors. 

528.  Lactose   (Milk-Sugar),  CIfHMOn   +  HaO,  is  ob- 
tained only  from  the  milk  of  the  mammalia,  to   which  it 
gives  the  sweetish  taste.     It  is   obtained  by  evaporating 
clarified  whey  till  it  crystallizes.     It  is  much  less  soluble, 
and  therefore  much  less  sweet,  than  cane-sugar,  and  its 
crystals  are  hard  and  gritty.     It  is  much  used  in  the  prep- 
aration of  homoeopathic  medicines. 

529.  Gum,  C19HMOn  (Arabin). — These    terms  are  ap- 
plied to  a  class  of  substances  which  are  often  seen  exud- 
ing in  globular  masses  from  the  bark  of  trees,  as  the  plum 
and  cherry.     Gum  is  translucent,  tasteless,  inodorous,  and 
either  dissolves  in  water,  cr  swells  up  and  forms  with  it  a 
thick  mucilage.     It  exists  in  small  proportion  in  the  cereal 
grains,  but  its  chief  source  is  certain  tropical  trees,  from 
the  bark  of  which  it  flows  in  such  quantity  as  to  be  gath- 
ered for  commercial  purposes.    Gum-arabic,  the  product  ol 
a  species  of  acacia,  is  a  hard,  brittle  substance,  and  is,  per- 
haps, the  best  known  of  the  gums.      Its  solution  being 
very  adhesive,  is  used  as  a  substitute  for  paste  or  glue. 
Mucilage  or  bassorin  is  a  kind  of  gum  insoluble  in  water, 
but  which  swells  into  a  gelatinous  mass  when  moistened. 
It  abounds  in   gum-tragacanth,   and  also  in   quince-seeds 
and  linseed.     Pectin,  or  the  jelly  of  fruits,  is  in  its  physi- 
cal properties  closely  allied  to  the   gums,  but  its  exact 
chemical  composition  has  not  yet  been  established  with 
certainty. 

Balsams  are  complex  substances  which  exude  from  the 
bark  of  certain  trees  ;  they  consist  for  the  most  part  of  an 
essential  oil  which  holds  in  solution  peculiar  substances 
known  as  resins.  Gum-copal,  mastic,  and  shellac,  belong 
to  this  class ;  they  are  insoluble  in  water,  but  dissolve  in 


SACCHARINE   BODIES. 


299 


FIG    195. 


alcohol,  naphtha,  and   oil  of  turpentine.      The  solutions 
thus  formed  constitute  varnishes. 

Caoutchouc,  or  India-rubber,  is  a  compound  of  hydrogen 
and  carbon,  of  great  value  to  the  chemist.  It  is  the  hard- 
ened juice  of  several  tropical  trees,  and  when  pure  is 
white.  Combined  with  sulphur  in  variable  proportions  it 
forms  the  vulcanized  caoutchouc  or  vulcanite  of  commerce. 

530.  Starch,    C6H10Oa.- 
This  substance  is  found  univer- 
sally distributed  in  the  vegeta- 
ble  kingdom   in   grains,  seeds, 
roots,  and  the  pith  and  bark  of 
plants.    When  pure  it  is  a  snow- 
white,  glistening  powder.     Ex- 
amined by  the  microscope,  it  is 
found  to  consist  of  exceedingly 
minute    round   or   oval   grains, 
which  vary  in  size  from  YJ-g-  to 
T_^_J.  of  an  inch  in  diameter. 
The  starch-granules  of  potatoes 
are  much  larger  than  those  of 
wheat   or    rice.       Starch-grains 
from  different  sources  vary  also 
in  form  and  structure.     Those 
of  the  potato  are  egg-shaped ; 
those  of  wheat  are  lens-shaped  ; 
those   of  rice   angular  ;    while 
several    kinds  have  a   grooved 
aspect,  and  consist  of  concen- 
tric layers,  like  the  coats  of  an 
onion.  As  each  variety  has  some 
peculiarity  by  which  it  may  be 
identified,    the    adulteration    of 
wheat-flour  by  potato,  or  other 
starches,  may  thus  be  detected. 

531.  Properties  and  Uses, — Starch  is  insoluble  in  cold 


Starch-Grains  of  Potatoes. 
FIG.  196. 


Ctarch-Grains  of  Plantain. 


FIG.  19T 


* 


Starch-Grains  of  Rice 


300  DESCRIPTIVE  CHEMISTRY. 

water,  alcohol,  and  ether,  but  swells  up  and  is  converted 
into  a  paste  in  water  containing  2  per  cent,  of  alkali.  If 
heated  in  water  to  140°  F.,  the  grains  swell  and  burst,  pro- 
ducing a  jelly-like  mass  (gelatinous  starch,  or  amadin), 
which  is  used  to  impart  a  gloss  to  textile  fabrics.  The 
test  of  starch  is  iodine,  which  combines  with  it,  forming  a 
blue  compound.  The  uses  of  starch  are  varied ;  the  most  im- 
portant, however,  is  that  of  nutrition,  the  comparative  value 
of  different  articles  of  vegetable  diet  depending  largely  on 
the  proportion  of  this  proximate  principle  which  they  con- 
tain. When  vegetable  food  is  prepared  for  the  table  by 
the  various  processes  of  cooking,  the  starch  is  slightly 
modified. 

532.  Dextrine. — When  commercial  starch  is  heated  un- 
der pressure  to  400°  F.  for  some  hours,  it  becomes  soluble 
in  cold  water,  and  is  changed  into  a  gurnmy  substance 
called  dextrine,  which,  under  the  name  of  British  gum,  has 
been  successfully  substituted  for  gum-arabic  by  calico- 
printers  in  thickening  their  colors.  Dextrine  is  also  pro- 
duced when  starch-paste  is  boiled  for  a  few  minutes  with 
weak  sulphuric  acid.  It  is  a  transparent,  brittle  solid,  iso- 
meric  with  starch,  soluble  in  water,  incapable  of  fermenta- 
tion, and  produces  right-handed  rotation  in  a  ray  of  polar- 
ized light;  hence  its  name.  When  solutions  of  dextrine 
are  boiled  with  dilute  acids  for  some  hours,  the  dextrine  is 
converted  into  glucose.  Dextrine  is  also  formed  from 
starch,  by  the  action  of  animal  secretions  such  as  saliva, 
bile,  and  pancreatic  juice. 

Glycogen,  C6H10O5,  was  first  obtained  by  Bernard  from 
the  livers  of  animals.  It  is  a  white,  amorphous,  starch-like 
substance,  odorless  and  tasteless,  and  is  converted  into 
glucose  by  boiling  with  dilute  acids,  or  by  contact  with 
blood,  saliva,  or  pancreatic  juice. 

Inulin  is  a  substance  obtained  from  the  roots  of  many 
plants,  among  which  are  the  dahlia,  dandelion,  and  chiccory. 
It  has  the  same  composition  as  common  starch,  but  differs 


SACCHARINE  BODIES.  301 

from  it  in  some  important  particulars.  Inulin  may  be  ob- 
tained by  washing  the  rasped  roots  on  a  sieve,  when  it  will 
settle  to  the  bottom  of  the  liquid.  It  is  a  white,  tasteless 
substance,  which  is  not  soluble  in  cold  water,  but  freely 
dissolves  by  the  aid  of  heat.  It  exists  in  the  plant  in  a 
liquid  form,  and  is  converted  by  the  action  of  dilute  acids 
into  laevulose.  Iodine  does  not  turn  inulin  blue. 

533.  Cellulose,  C18H30O1B  (  Woody  Fibre,  Lignine).—^^ 
is  the  most  abundant  product  of  vegetation.    Besides  form- 
ing the  chief  bulk  of  all  trees,  it  exists  in  the  straw  and 
stalks  of  grain,  in  the  membrane  which  envelops  the  kernel 
(bran),  in  the  husk  and  skin  of  seeds,  and   in  the  rinds, 
cores,  and  stones  of  fruit.     Wood  consists  of  slender  fibres, 
or  tubes  closely  packed  together.    When  first  formed  these 
tubes  are  hollow  and  serve  to  convey  the  sap,  but  in  the 
heart- wood  of  trees  they  become  filled  up  and  consolidated, 
the  circulation  of  fluids  taking  place  in  the  white  external 
sap-wood  (alburnum).     Upon  the  density  with  which  the 
fibres  are  imbedded  depends  the  property  of  hardness  or 
softness  of  wood.     Cellulose  is  the  fibrous  portion  of  the 
woody  tissue. 

534.  Properties  and  Uses.— The  properties  of  cellulose 
may  be  conveniently  studied  in  fine  linen  and  cotton,  which 
are  almost  entirely  composed  of  it.     When  pure  it  is  taste- 
less, insoluble  in  water  and  alcohol,  and  not  sensibly  af- 
fected by  boiling  water.     By  cold  concentrated  sulphuric 
acid,  it  is  converted  into  dextrine.     The  uses  of  cellulose 
are  almost  numberless.      It  forms  the  chief  bulk  of  the 
wood  we  burn,  of  the  linen  and  cotton  fabrics  we  wear,  and 
of  the  paper  we  write  and  print  upon.     Besides  these  uses 
of  unaltered  cellulose,  a  multitude  of  useful  chemical  bodies 
are  derived  from  its  decomposition ;  charcoal,  illuminating 
gas,  tar,   wood-spirit,   wood-vinegar,  creosote,  and  oxalic 
acid,  being  among  the  most  important.     Grape-sugar  and 
alcohol  have  also  been  made  from  it. 

535.  Pyroxylene. — If  pure  cellulose  (C18H30O15),  as  cot- 


302  DESCRIPTIVE   CHEMISTRY. 

ton,  linen,  sawdust,  or  paper,  be  steeped  for  a  few  minutes 
in  a  mixture  of  nitric  and  sulphuric  acids,  then  squeezed, 
washed,  and  dried  by  gentle  heat,  a  part  of  the  hydrogen 
of  the  cellulose  is  oxidized  by  the  action  of  the  nitric  acid, 
and  eliminated  as  water,  while  its  place  in  the  compound  is 
occupied  by  a  corresponding  quantity  of  the  radicle  nitryl 
(NO0).  This  quantity  is  greater  in  proportion  to  the  con- 
centration of  the  acid.  When  a  mixture  of  concentrated 
sulphuric  acid  with  nitric  acid  of  1.52  specific  gravity  is 
used,  pyroxyline,  C18HQ1  (N2O2)9  O1B,  a  highly-explosive  com- 
pound, is  produced,  which  constitutes  the  well-known  gun- 
cotton,  discovered  a  few  years  ago  by  Prof.  Sch5nbein.  It 
ignites  at  400°  F.  (200°  below  gunpowder),  and  disappears 
in  an  instantaneous  flash,  leaving-  hardly  a  trace  of  residue. 
Authorities  vary  in  estimating  its  explosive  force,  but  the 
latest  make  it  about  three  times  that  of  gunpowder.  The 
extreme  suddenness  of  the  propulsive  force  overstrains  the 
gun  and  produces  less  effect  upon  the  ball  than  gunpowder. 
Collodion  is  formed  by  dissolving  gun-cotton  in  ether, 
containing  a  small  proportion  of  alcohol.  On  evaporating 
the  ether,  a  transparent,  adhesive  film  is  left,  which  is  in- 
soluble in  water  and  is  used  in  surgery  for  protecting 
wounds  from  the  air.  The  chief  use  of  collodion,  however, 
is  in  photography. 

§  4.  Fermentation. 

536.  When  certain  compound  substances,  derived  chief- 
ly from  plants  and  animals,  are  exposed  to  the  action  of  air 
and  water,  at  a  given  temperature,  they  undergo  decompo- 
sition, which,  when  involving  the  formation  of  useful  prod- 
ucts, is  generally  known  as  fermentation,  but  when  result- 
ing in  the  production  of  useless  and  ill-flavored  bodies  is 
distinguished  as  putrefaction.  These  changes  all  agree  in 
having  a  peculiar  self-sustaining  and  contagion-like  charac- 
ter. The  true  nature  of  these  processes  is  not  yet  thor- 
oughly understood.  But  careful  investigation  has  shown. 


FERMENTATION.  303 

that,  in  by  far  the  largest  number  of  cases,  we  may  recog- 
nize the  presence  of  living  organisms.  The  exciting  cause 
of  fermentation  has  been  sought  in  the  oxygen  of  the  air, 
but  it  appears  from  recent  experiments  that  air  which  has 
been  passed  through  a  red-hot  tube  does  not  induce  fer- 
mentation even  in  those  bodies  which  are  most  liable  to 
this  change.  It  has  been  proved,  however,  that  ordinary 
air  contains  the  germs  of  microscopic  plants  and  animals, 
and  it  seems  almost  certain  that  the  excitation  of  the  pro- 
cesses in  question  is  due  to  their  action. 

537.  Ferments  and  Fermentable  Bodies.  —  The  sub- 
stances most  disposed  to  putrefaction  are  certain  compounds 
rich  in  nitrogen,  contained  largely  in  flesh,  blood,  cheese, 
milk,  white  of  egg,  gelatine,  and  other  animal  products. 
These  bodies  require  only  the  presence  of  water,  and  free 
access  of  air  at  the  commencement,  to  induce  in  them  a 
process  of  decomposition.  Of  those  compounds  which  con- 
tain no  nitrogen  there  are  but  few,  as  for  example  sugar, 
gum,  and  starch,  that  may  be  brought  into  a  state  of  fer- 
mentation by  mere  contact  with  air  and  water.  But  many 
substances,  incapable  of  fermenting  by  themselves,  undergo 
that  change  when  brought  in  contact  with  a  minute  quan- 
tity of  the  above-mentioned  nitrogenous  bodies.  The  lat- 
ter are,  for  this  reason,  termed  ferments,  the  former  fer- 
mentable bodies. 

As  a  spark  may  kindle  a  conflagration  that  shall  con- 
sume a  city,  so  the  minutest  quantity  of  fermenting  or  pu- 
trescent  matter  is  often  sufficient  to  affect  an  indefinite 
quantity  of  changeable  substance.  The  remarkable  com- 
municability  of  these  effects  is  well  observed  in  the  action 
of  leaven  upon  dough.  It  is  also  painfully  illustrated  by 
physicians,  who  sometimes  wound  themselves  while  dissect- 
ing. The  small  trace  of  decomposing  matter  from  the  dead 
body  which  clings  to  the  dissecting-knife  is  sufficient  to 
establish  a  rapid  decomposition  in  the  living  system,  which, 
in  many  cases,  quickly  terminates  in  death. 


304  DESCRIPTIVE   CHEMISTRY. 

The  part  played  by  yeast,  and  the  nature  of  vinous  fer- 
mentation, has  been  a  matter  of  much  speculation.  Yeast 
consists  of  round  or  egg-shaped  cells  about  ToVg-  °f  a  m^~ 
lirnetre  in  diameter ;  these  consist  of  an  outer  wall  of  cellu- 
lose, inclosing  a  liquid.  The  yeast-cells  grow  and  multiply 
in  a  fermenting  liquid,  but  the  presence  of  nitrogen,  phos- 
phorus, sulphur,  potassium,  and  magnesium,  in  combined 
form,  seems  to  be  necessary  to  their  growth.  Several  dif- 
ferent kinds  or  modes  of  fermentation  have  been  observed, 
varying  in  the  character  of  the  products  formed.  The  pro- 
cesses are,  moreover,  very  much  modified  by  temperature 
and  other  atmospheric  conditions.  The  modes  of  fermen- 
tation best  known  are  the  vinous,  acetous,  lactous,  and  sac- 
charous. 

538.  Vinous  Fermentation. — When  the  sweet  juice  of 
fruits  or  plants  is  exposed  to  the  air  at  the  temperature  of 
70°  or  80°  F.,  in  the  course  of  a  few  hours  a  change  com- 
mences :  small  bubbles  consisting  of  carbonic  dioxide  rise 
to  the  surface,  the  liquid  becomes  turbid,  and  begins  to 
ferment,  or,  as  is  commonly  said,  to  "  work"     After  a  time 
the  bubbles  cease  to  rise  and  the  liquid  is  no  longer  sweet, 
but  has  acquired  a  spiritous  taste.     If,  now,  it  be  distilled, 
an  inflammable  body  is  separated,  which  is  known  as  spirits 
of  wine,  or  alcohol,  a  product  of  the   decomposition  of 
sugar.     Besides  the  alcohol  the  fermented  liquid  generallv 
contains  two  other  bodies,  known  respectively  as  glycerine 
and  succinic  acid.     Other  compounds  are  also  in  some  in- 
stances produced. 

539.  Saecharous  Fermentation. — But  sugar  itself  may 
be  a  product  of  fermentation.     When  seeds  are  exposed 
to  air  and  moisture  at  a  suitable   temperature,  germina- 
tion commences.     This  consists  in  a  series  of  changes,  of 
which  the  first  is  an  alteration  of  a  portion  of  the  nitro- 
genous matter  and  the  production  of  a  compound  not  well 
understood,  called  diastase.    This  is  an  active  ferment,  and, 
taking  effect  upon  the  starch,  changes  it  to  sugar  and  dex- 


ETHERS  AND  ALDEHYDES.  305 

trine.  When  barley  is  treated  in  this  way  it  swells  and 
becomes  sweet.  Diastase  is  formed,  and  the  barley  is 
termed  malt.  When  the  germ  is  about  half  an  inch  long 
the  process  is  arrested  by  heat,  but  the  dextrine  is  not 
destroyed. 

540.  Acetous  Fermentation. — If  the  vinous  fermenta- 
tion is  not  checked  at  the  proper  time,  it  passes  on  to  a 
second  stage,  the  acetous  fermentation  ;  the  liquid  loses  its 
spirit  and  quality,  and  becomes  sour.     Oxygen  is  absorbed, 
and  the  alcohol   converted    into  vinegar  or   acetic   acid, 
C,H4O9.      Pure  diluted  alcohol  does  not  absorb  oxygen 
when  exposed  to  the  atmosphere ;   it  is  affected  only  by 
adding  some  matter  in  a  state  of  change,  or  which  absorbs 
oxygen.     The  action  proceeds  slowly  at  first,  but  by  de- 
grees a  peculiar  body,  a  kind  of  slimy  vegetable  mould,  is 
formed,  which  is  known  as  mother  of  vinegar,  and  which 
acts  something  like  a  ferment  to  hasten  the  process.     It  is 
supposed  that  this  acetous  ferment  acts  as  a  carrier  of 
atmospheric  oxygen,  which   it  absorbs  within  its  pores, 
thus  bringing  it  into  intimate  contact  with  the  alcohol.  In 
this  respect  the  action  of  the  ferment  is  like  that  of  plati- 
num, which  causes   the  union   of  oxygen  and  hydrogen, 
when  these  gases  are  condensed  within  its  pores. 

§  5.  Ethers  and  Aldehydes. 

541.  The  ethers  may  be  regarded  as  oxides  of  the  alco- 
hol radicles,  and  they  bear  the  same  relation  to  the  alcohols 
that  metallic  oxides  bear  to  the  metallic  hydrates,  thus : 

C.H. 


a  i 


c,c  CH 

Ethylic  Oxide.  Ethylic  Hydrate. 

(Ethylic  Ether.)  (Ethylic  Alcohol.) 

Ethylic  Ether,  C4H10O  (Sidphuric  Ether).— When  equal 
weights  of  strong  sulphuric  acid  and  alcohol  are  heated  in 
a  retort,  a  yapor  passes  over  which  may  be  condensed  into 


306 


DESCRIPTIVE   CHEMISTRY. 


a  limpid  fluid,  called  ether  from  its  volatility,  and  sulphuric 
ether,  because  in  obtaining  it  sulphuric  acid  is  employed. 
Ether  is  colorless,  with  a  fragrant  odor,  a  hot,  pungent 
taste,  and,  when  inhaled,  produces  insensibility  to  pain  ; 
hence  it  is  much  used  as  an  anaesthetic.  It  is  so  vola- 
tile that  it  disappears  when  poured  through  the  air  from 
one  vessel  to  another,  and,  when  placed  upon  the  hand, 
produces  cold  by  rapid  evaporation.  It  boils  at  96°  Fahr., 
or  when  exposed  to  the  air  in  summer,  and  is  very  com- 
bustible, burning  with  more  light  than  alcohol  and  some 
smoke.  Its  vapor,  when  mixed  with  air,  is  explosive.  It 
readily  dissolves  fats  and  oils. 

542.  Aldehydes. — The  aldehydes  are  a  class  of  com- 
pounds intermediate  between  acids  and  alcohols,  and  they 
are  produced  by  the  oxidation  of  the  latter.  Example, 
acetic  aldehyde : 

HO 
H-C-C 


FIG.  198. 


Acetic  aldehyde,  C3H4O,  the  best  known 
compound  of  this  series,  may  be  produced  by 
the  gradual  oxidation,  in  various  ways,  of  or- 
dinary alcohol,  or  by  transmitting  a  mixture 
of  alcohol  and  air  through  a  porcelain  tube 
at  a  low  red  heat.     When  a  few  drops  of  al- 
cohol are  placed   in   a    cup,   its    vapor   will 
mingle  with  the  air.     If,  now,  a  red-hot  coil 
of  platinum  wire  be  introduced  into  the  cup, 
Fig.  198,  the  oxidation  of  the  vapor  com- 
mences, pungent  odors  of  acetic  aldehyde  are 
given  off,  and  the  wire  is  kept  at  a  red  heat  by  the  con- 
tinued oxidation.     If  the  coil  be  suspended  over  the  wick 
of  an  alcohol  or  ether  lamp,  Fig.  199,  it  will  continue  to 
glow  for  hours  after  the  flame  is  extinguished,  from  the 


ETHERS  AND  ALDEHYDES.  307 

same  cause.      Acetic  aldehyde  is  a  highly-         FlG- 199- 
volatile,  inflammable  liquid,  with  a  pungent, 
apple-like  odor. 

543.  Camphor,  C10H16O. — This  well-known 
substance  has  the  composition  of  an  aldehyde, 
but  its  reactions  are  different  from  .the  other 
aldehydes.  It  is  obtained  by  distilling  the 
wood  of  the  camphor- tree  (found  in  Japan 
and  other  parts  of  the  East)  with  water,  and 
collecting  the  vapors  in  a  vessel  containing  rice-straw. 
It  condenses  in  the  straw  and  is  again  sublimed,  after 
which  it  is  thrown  into  commerce ;  but  it  requires  subse- 
quent purifications  to  fit  it  for  use.  Camphor  is  quite  vola- 
tile and  readily  soluble  in  alcohol,  with  which  it  forms  a 
solution  known  as  spirits  of  camphor.  Taken  in  large 
doses  it  acts  as  a  poison. 

544.  Chloral,  C,HC13O. — By  replacing  a  single  atom  of 
the  hydrogen  in  the  formula  of  aldehyde,  by  chlorine,  the 
formula  for  a  compound  known  as  chloral  is  obtained.     It 
is  formed  by  the  action  of  pure  and  dry  chlorine  gas  on 
absolute  alcohol.     It  is  a  thin,  colorless  oil,  which  boils  at 
about  96°  C.     It  has  a  peculiar,  pungent  odor,  and  excites 
a  copious  flow  of  tears.     Its  taste  is  greasy,  and  slightly 
astringent.      The  vapor  acts    powerfully  upon   the   skin. 
Mixed  with  a  small  quantity  of  water  it  becomes  heated 
and  solidifies  to  a  white  crystalline  mass,  chloral  hydrate, 
which  is  soluble  in  a  large  quantity  of  water,  volatilizes 
gradually  in  the  air,  and  may  be  distilled  without  decom- 
position.    It  has  been  recentty  introduced  into  medicine, 
as  a  means  of  producing  sleep. 

545.  Chloroform,  CHC13,  is  prepared  by  distilling  alco- 
hol with  a  solution  of  chloride  of  lime.      It  is  a  colorless, 
volatile  liquid,  of  a  strong,  agreeable  odor,  and  a  sweet, 
penetrating  taste.      It  dissolves  sparingly  in  water,  but 
freely  in  alcohol  and  ether.     It  is  extensively  employed  in 
medicine,  but  for  this  purpose  it  should  be  perfectly  pure, 


308  DESCRIPTIVE  CHEMISTRY. 

as  the  fatal  effects  which  have  sometimes  attended  its  use 
are  doubtless  chiefly  owing  to  its  contaminations.  It 
should  be  colorless  acd  free  from  a  chlorous  smell,  or  any 
unpleasant  odor,  when  a  few  drops  are  evaporated  on  the 
hand. 

Chloroform  is  one  of  the  most  important  representatives 
of  a  class  of  bodies,  the  vapor  of  which  when  inhaled  pro- 
duces temporary  insensibility  to  pain,  or  ancesthesia  /  these 
substances  are  known  as  anaesthetics. 


CHAPTER   XXVI. 

ORGANIC   CHEMISTRY    (CONTINUED). 

§  1.  Acids. 

546.  A  LARGE  number  of  organic  acids  are  known,  some 
of  which  exist  in  a  free  state,  as,  for  example,  formic  acid, 
which  is  secreted  by  ants  and  'is  found  in  nettles.     These 
compounds  constitute  several  series,  which  are  all   regard- 
ed as  derived  more  or  less  directly  from  the  hydrocarbons. 
Formic  acid,  CH2Oa,  is  a  clear,  pungent,  volatile,  strongly 
acid  liquid,  which  was  first  obtained  by  distilling  the  bod' 
ies  of  red  ants  (Formica  rubra)  in  water,  hence  its  name 
formic  acid.     It  is  also  found  in  human  blood,  urine,  and 
other  secretions,  in  the  juices  of  many  plants,  and  in  the 
waters  of  certain  mineral  springs. 

547.  Acetic  Acid,  C2H4O2. — This  acid  is  one  of  the  most 
important  organic  compounds.  /It  is  the  essential  constitu- 
ent of  vinegar,  which  is  merely  ashore  or  less  impure  solution 
of  acetic  acid,  common  table-vijfegar  containing  from  three 
to  four  per  cent.     Pure  acetic  swid  is,  at  ordinary  tempera- 
tures, a  colorless,  intensely  souifc  liquid,  having  a  pungent 
odor,  and  capable  of  raising  a  brfeter  on  the  skin.    It  solidi- 


ACIDS.  309 

fies  at  or  below  17°  C.  to  a  crystalline,  ice-like  body,  known 
as  "  glacial  acetic  acid,"  and  boils  at  about  119°  C.  Vine 
gar  is  usually  obtained  by  the  spontaneous  oxidation  of 
dilute  alcoholic  liquors,  saccharine  solutions,  etc.  If,  in 
the  process  of  its  manufacture,  the  air  comes  in  contact 
with  only  a  small  portion  of  the  liquid,  months  may  be  re- 
quired to  produce  the  change.  Wdod-vinegar,  or  pyrolig- 
neous  acid,  is  obtained  by  the  destructive  distillation  of 
wood,  dry  beech-wood  being  the  best,  a  pound  yielding 
nearly  half  a  pound  of  the  acid.  It  is  a  brown  liquid,  with 
a  strong  smoky  taste  and  odor.  It  is  extensively  used  to 
form  salts — the  acetates  used  by  dyers. 

548.  Butyric  Acid,  C4H8O2,  is  prepared  by  allowing  a 
mixture  of  sugar,  chalk,  and  cheese,  to  ferment.      It  is 
found  in  small  quantity  in  butter,  in  perspiration,  in  some 
plants,  and   in  the   juice  of  human  flesh.      It   resembles 
acetic  acid  in  appearance,  has  a  peculiar  rancid  odor,  and 
is  soluble  in  water. 

Glycocholic  Acid,  CaH4O3,  constitutes  the  great  mass 
of  the  resinous  matter  of  ox-bile;  it  forms  silky  white, 
needle-shaped  crystals,  of  a  bitter-sweet  taste,  which  are 
soluble  in  water  and  alcohol,  and  have  an  acid  reaction. 

549.  Lactic  Acid,  C8HflO3.— This  acid  is  so  called  be- 
cause it  occurs  in  sour  milk.     It  is  formed  from  sugar  by 
lactic  fermentation,  and   is  a  colorless,  sirupy,  very  acid 
liquid.     Succinic  acid,  C4H6O4,  is  also  one  of  the  products 
of  the  fermentation  of  sugar  (538),  and  is  obtained  by  the 
distillation  of  amber.     It  occurs  in  certain  resins,  in  worm- 
wood,  and   in   small  quantities   in   animal    juices.      Inti- 
mately connected  with  this  Jacid  are  two  of  much  impor- 
tance, viz.,  malic  acid,  C4HA6,  and  tartar ic  acid,  C4HeO6. 
The  former  is  found  in  mai  acid  fruits  and  in  the  stalks 
of  rhubarb,  but  is  usually  (•ained  from  the  unripe  berries 
of  the  mountain-ash.      ItS  a  colorless   solid,   dissolves 
readily  in  water  and  alcohoind  crystallizes  with  difficulty. 
The  solutions  of  all  the  Jjfas  named  have  an  agreeable 


310  DESCRIPTIVE   CHEMISTRY. 

acid  taste,  but  become  mouldy  if  long  kept,  and  gradually 
undergo  decomposition. 

Tartaric  acid  is  found  abundantly  in  the  juices  of  many 
fruits.  It  is  obtained  by  the  decomposition  of  calcic  tar- 
trate  with  sulphuric  acid.  Its  crystals,  when  pure,  are 
colorless,  transparent,  permanent  in  the  air,  and  dissolve 
readily  in  water  or  alcohol.  It  is  extensively  used  by  the 
calico-printer  and  dyer  for  the  removal  of  mordants. 
Mixed  with  the  bicarbonates  of  the  alkalies,  it  forms  the 
soda-powders  of  effervescing  draughts. 

550.  Benzoic  Acid,  C7H6O2,  obtained  exclusively  at  one 
time   from  gum-benzoin,  is  now   procured  from  hippuric 
acid,  which  occurs  in  the  urine  of  herbivorous  animals. 

551.  Salicylic  Acid,  C6H4  OH  CO2H,  is  one  of  the  deriva- 
tives of  salicine,  which  is  a  neutral  vegetable  principle, 
discovered  in  1830  in  the  bark  of  the  willow,  Salix,  whence 
its  name.     The  acid  was  early  obtained  from  the  flowers 
of  the  meadow-sweet  (Spirea  ulmarid),  and  it  occurs  in 
the  oil  of  winter-green.     It  is  now  regarded  with  great 
interest,  on  account  of  its  valuable  qualities  as  an  anti- 
ferment  and  antiseptic.      As  its   practical  value  became 
known,  the  sources  from  which  it  had  been  obtained  were 
found  utterly   inadequate  to  the   increased  demand;  and 
the  reconstructive  power  of  the   modern  chemist  sought 
for  a  compound,  which  might  be  split  up,  or  reorganized 
in  such  a  way  as  to  yield  the  desired  salicylic  acid.     The 
German  chemists  found  this  in  phenol  or  carbolic  acid,  a 
substance  long  known  for  its  valuable  qualities  as  an  anti- 
ferment.     The  agent  selected  to  reconstruct  the  molecule 
of  phenol  was  carbonic  dioxidl    The  pure  acid  is  obtaii 

in  minute  acicular  crystals,  white,  odorless,  and  nej 
tasteless  ;  insoluble  in  cold  Biter,  more  soluble  in  hot 
water,  and  in  still  greater  d»ee  soluble  in  alcohol  and 
ether.  It  melts  at  about  25™ F.  It  is  used  in  medicine 
and  in  surgical  operations,  wh^fc  it  is  said  to  be  more  effec- 
tive in  smaller  quantities  thanBiy  other  antiseptic,  and  to 


ACIDS.  311 

be  devoid  of  all  irritating  action  upon  the  living  tissues. 
Tn  cases  of  decomposition  which  cannot  be  reached  by  any 
other  antiseptic,  salicylic  acid  is  claimed  to  be  especially 
valuable. 

552.  Citric  Acid,  C6H8O7,  is  found  principally  in  fruits 
of  the  orange  family,  but  is  of  frequent  occurrence  in  goose- 
berries, currants,  and  other  acid  fruits.     It  may  be  readily 
procured  from  the  juice  of  the  lemon  by  the  aid  of  chalk 
and  sulphuric  acid.     It  has  a  pleasant  acid   taste,  is  very 
soluble  in  water,  and  is  used  in  medicine,  calico-printing, 
and  for  effervescing  draughts.      Gallic  acid,  C7H,O6,  oc- 
curs in  sumach,  acorns,  tea,  and  many  plants.     It  crystal- 
lizes in  silky  needles,  is  freely  soluble  in  boiling  water,  and 
does  not  precipitate  gelatine.     Heated  to  about  215°  C., 
gallic  acid  is  decomposed  into  carbonic  dioxide  and  pyro- 
gallol,  C6H6O3.     This  acid  is  extensively  used  in  photog- 
raphy.     Both  gallic  acid  and   pyrogallol  decompose  the 
salts  of  silver,  gold,  and  platinum  ;  hence  they  are  exten- 
sively employed  in  photography,  and  in  the  manufacture 
of  hair-dves. 

553.  Tannins  (Tannic  Acids). — There  are  several   dis- 
tinct compounds  known  under  the  Dame  tannin,   which 
resemble  each  other  in  character  and  possess  an  acid  reac- 
tion.    They  are  found  extensively  diffused  throughout  the 
vegetable  kingdom,  and  are  all  distinguished  by  an  astrin- 
gent taste.     The  bark  and  leaves  of  most  forest-trees,  as 
well  as  of  many  fruit-trees,  contain  a  large  quantity  of 
tannin  ;  it,  is  found  in  various  roots,  shrubs,  and  seeds,  and 
is  the  astringent  principle  of  tea  and  coffee.     The  most 
important  of  these   compounds,  obtained    from   gall-nuts, 
is  generally  known   as  gallotannic  acid,   C27H22O17.      It 
has   an  intensely  astringent   taste,  reddens  litmus-paper, 
and  is  very  soluble  in  water.     When  a  solution  of  gal- 
lotannic  acid  is   mixed  with  a  solution  of  a  ferric  com- 
pound, it  produces  a  deep  bluish-black  precipitate,  which 
is  the  basis  of  writing-ink.    The  gradual  darkening  of  pale, 

14 


312  DESCRIPTIVE  CHEMISTRY. 

watery  ink  is  due  to  the  oxidation  of  the  iron  it  contains. 
Tannins  form  insoluble  compounds  with  starch,  gelatine, 
and  other  organic  bodies,  the  most  remarkable  being  those 
with  gelatine,  which  form  the  basis  of  leather. 

554.  Oxalic  Acid,  C2H2O4,  is  met  with  in  the  juice  of 
the  sorrel,  rhubarb,  and  many  plants,  sometimes  in  the  free 
state,  but  more  frequently  in  the  compound  known  as  calcic 
oxalate.    It  is  commonly  prepared  by  the  oxidation  of  sugar 
or  starch  with  nitric  acid  :  one  part  of  sugar  is  dissolved  in 
eight  parts  of  nitric  acid,  and  gently  heated,  when  intense 
action  ensues,  with  a  copious  disengagement  of  nitrous  acid 
fumes.    By  evaporating  the  solution,  oxalic  acid  may  be  ob- 
tained in  large,  transparent,  and  intensely  sour  crystals. 
Oxalic  acid  is  poisonous,  and  its  crystals  resemble  those 
of  Epsom  salts,  for  which  it  is  sometimes  mistaken.     In 
cases  of  poisoning  with  it,  chalk  or  magnesia,  mixed  in 
water,  is  the  proper  antidote.     Oxalic  acid  is  largely  used 
in  calico-printing  ;  it  is  also  employed  as  a  delicate  test 
for  the  presence  of  lime,  with  which  it  forms  an  insoluble 
salt.    It  removes  ink  and  iron  stains  from  linen  by  forming 
a  soluble  oxalate  of  iron,  but  the  acid  is  so  corrosive  as  to 
injure  the  fibre  if  not  immediately  removed  by  washing. 

555.  Alkaline  Organic  Salts.— The  compounds  of  this 
group  are  derived  from  the  organic  acids  by  the  substitu- 
tion of  a  radicle  of  the  Lithium  group  for  the  basic  hydro- 
gen of  the  acid.    The  most  important  salt  of  the  acid  series 
is  hydro-potassic  tartrate  (cream  of  tartar),  (HK),  (C4H4O4) 
O3.     It  is  deposited  in  an  impure  state  from  wine  consti- 
tuting the  tartar  or  argol  of  commerce.    When  purified  by 
recrystallization,  it  forms   a  white  crystalline  powder,  or 
larger  crystals,  soluble  with  difficulty  in  cold  water,  more 
readily  in  hot  water,  and  possessing  a  pleasant  sour  taste. 
Among  the  salts  of  the  neutral  series,  sodio-potassic  tartrate 
(Rochelle  salts),  (NaK)  (C4H4O4)  Oa  +  4  H2O,  deserves  spe- 
cial notice.     It  is  obtained  in  beautiful  large  crystals,  per- 
fectly colorless  when  pure,  of  mild  saline  taste,  by  crystal- 


ORGANIC  ALKALOIDS.  313 

lizing  mixed  solutions  of  argol  and  soda-ash.  It  is  largely 
used  in  medicine,  forming  the  chief  constituent  of  Seidlitz 
powders. 

§  2.   Organic  Alkaloids. 

556.  The  term  alkaloid  has  been  applied  to  a  large 
number  of  bodies  having  the  general  constitution  of  amines. 
They  contain  carbon,  oxygen,  hydrogen,  and  nitrogen,  and 
act  as  bases.     Many  compounds  analogous  to  these  have 
been  artificially  prepared,  but  the  vegetable  alkaloids  have 
as  yet  defied  the  constructive  power  of  the  chemist.     They 
include  some  of  our  most  violent  poisons,  and  act  power- 
fully on  the  animal  economy.     Most  of  the  alkaloids  dis- 
solve sparingly  in  water,  but  freely  in  boiling  alcohol ;  are 
intensely  bitter,  and  usually  restore  the  reddened  color  of 
litmus.     They  are  the  most  powerful  medicines  and  poi- 
sons known.      Gallotannic  acid  precipitates  most  of  the 
organic  bases,  forming,  with  them,  insoluble  compounds ; 
hence  it  is  an  excellent  antidote  when  they  have  been 
taken  in  poisonous  doses.     We  shall  notice  only  the  more 
important  alkaloids  found  in  vegetable  substances. 

557.  Nicotine,   C10H14N9. — This  compound  is  of  inter- 
est, as  the  chief  alkaloid  contained  in  the  smoke  of  tobacco, 
and,  in  fact,  is  the  proximate  cause  of  the  narcotic  effects 
produced  by  the  use  of  that  plant,  which  contains  it  in 
quantities  varying  from  two  to  eight  per  cent.     It  is  a 
colorless,  transparent  oil,  which  boils  at  250°  C.,  giving 
off  very  irritating  vapors.     It  is  soluble  in  water,  alcohol, 
and  oils.     It  has  a  burning  taste,  even  when  much  diluted, 
and  is  one  of  the  most  violent  poisons  known.     The  effect 
is  said  to  be  produced  upon  the  motor  nerves,  producing 
convulsions,  and  afterward  paralysis.     Five  milligrammes 
has  been  found  sufficient  to   kill  a   medium-sized  dog  in 
three  minutes. 

558.  Morphine,  C17H19O3N. — This  is  the  chief  active  prin- 
ciple of  opium,  which  is  the  hardened,  milky  juice  of  the 


314  DESCRIPTIVE   CHEMISTRY. 

poppy.  Opium  is  a  very  complex  body,  containing,  besides 
morphine,  a  large  number  of  other  alkaloids.  Morphine 
(from  Morpheus,  in  consequence  of  its  sleep-inducing  prop- 
erty) is  a  crystallizable,  resin-like  body,  without  odor,  and 
possessing  a  bitter,  disagreeable  taste.  It  is  a  powerful  nar- 
cotic and  poison,  and,  in  the  form  of  the  acetate,  sulphate, 
and  hydrochlorate,  is  largely  used  in  medicine.  Piperine, 
C17H19NO3,  is  a  substance  isomeric  with  morphine,  found  in 
common  black  and  white  pepper.  It  is  nearly  insoluble  in 
cold  water,  has  an  acrid  taste,  and,  when  acted  upon  by 
nitric  acid,  develops  an  odor  of  bitter-almonds.  Capsicine 
is  an  alkaloid  obtained  from  Cayenne  pepper.  It  forms 
crystallizable  salts,  with  acetic,  nitric,  and  sulphuric  acids. 

559.  Strychnine,  C21H22O2N2,  is  chiefly  obtained  from  the 
beans  of  the  strychnos  nux-vomica,  a  small  East  India 
tree,  but  is  found  in  several  other  plants  belonging  to  that 
tribe.     Cold  water  dissolves   only  ^-^QQ  of  its  weight  of 
strychnine,  but  it  is  more  readily  soluble  in  essential  oils 
and  chloroform.     From  its  solutions  it  crystallizes  in  small 
brilliant  octahedrons,  of  exceedingly  bitter  taste.     Such  is 
its  intense  bitterness,  that  it  imparts  it  perceptibly  to  700,- 
000  times  its  weight  of  water.    It  is  a  deadly  poison,  ^  of 
a  grain  killing  a  dog  in  thirty  seconds.    It  takes  effect  upon 
the  nerve-centres  of  the  spinal  axis,  producing  fearful  con- 
vulsions.    The  terrible  woorara  poison,  with  which   the 
South  American  natives  poison  their  arrows,  and  which  has 
been  lately  used  as  a  remedy  for  tetanus,  appears  to  con- 
tain a  principle  nearly  allied  if  not  identical  with  strych- 
nine.    Jlracine  is  an  alkaloid  closely  allied  to  strychnine, 
and  obtained  from  the  same  genus  of  plants. 

560.  Quinine,  C90HQ4O3N2,  is  extracted  from  pulverized 
Peruvian  bark  by  acidulated  water.     It  is  a  white,  crystal- 
line substance,  which  unites  with  acids,  producing  intensely 
bitter  salts.     Quinine  sulphate,  which  forms   light,  bulky 
crystals,  is  the  salt  employed   in  medicine.      It  dissolves 
sparingly  in  water,  but  freely  in  dilute  sulphuric  acid  and 


ALBUMINOUS  SUBSTANCES.  315 

alcohol.  Cinchonine  is  another  alkaloid  from  the  same 
source. 

561.  Caffeine  Series. — Two  terms  of  this  series  are  known. 
Tkeobromine,  C7H8O2N4,  is  a  crystalline  alkaloid,  obtained 
from  cacao-beans,  the  source  of  chocolate.  Caffeine  or 
theine,  C8H10O2N4,  is  an  alkaloid,  which  may  be  obtained 
from  coffee,  tea,  and  several  other  plants,  the  stimulating 
effects  of  which  are  in  part  due  to  the  presence  of  caffeine 
compounds.  Coffee  seldom  contains  more  than  one  per 
cent,  cf  the  principle,  while  tea  furnishes  three  or  four. 
Caffeine  crystallizes  in  long,  flexible,  silky  needles,  has  a 
slightly  bitter  taste,  and  dissolves  sparingly  in  cold  water, 
but  freely  in  hot  water. 

The  stimulating  effects  of  coffee  and  tea  are,  however, 
not  due  to  the  caffeine  alone,  but  are  modified  by  various 
other  ingredients.  In  tea,  the  alkaloid  is  associated  prin- 
cipally with  tannin  and  an  essential  cil ;  in  coffee,  with 
empyreumatic  and  essential  oils. 

§  3.  Albuminous  Substances. 

562.  Under  this  head  are  classed  a  number  of  com- 
pounds, some    of  which    form    essential   portions   of  the 
bodies  of  animals,  and  occur  in  certain  parts  of  vegetables ; 
while  others,  not  properly  albuminoids,  are  obtained,  di- 
rectly or  indirectly,  from  the  animal  organism.     The  albu- 
minoids possess  constitutions   very  complicated,  and  our 
knowledge  of  their  chemical  relations  is  limited.     They  do 
not  crystallize,  but  are  found  in  amorphous,  jelly-like  form. 
They  contain,  in  addition  to  carbon,  oxygen,  hydrogen, 
and  nitrogen,  small  quantities  of  sulphur  and  phosphorus. 
Strong  mineral  acids  dissolve  all  of  the  albuminoids. 

563.  Albumen  is  the  chief  and  characteristic  constituent 
of  the  serum  of  the  blood,  and  of  white  of  egg,  and  occurs 
in  all  the  fluids  which   supply  nutritive  material  for  the 
renovation  of  the  animal  tissues.     It  forms    about  seven 


316  DESCRIPTIVE   CHEMISTRY. 

per  cent,  of  blood,  and  twelve  per  cent,  of  the  white  of  egg. 
Albumen  exists  in  two  modifications — the  soluble  form, 
and  the  insoluble  variety  into  which  it  may  be  brought  by 
the  action  of  heat,  as  when  white  of  egg  is  boiled.  These 
two  modifications  are  identical  in  chemical  composition, 
and  the  difference  is  thought  to  be  due  to  the  presence  of 
certain  mineral  salts  which  are  associated  with  the  soluble 
variety.  A  solution  of  albumen,  heated  to  72°  C.,  is  co- 
agulated. 

Vegetable  albumer  abounds  in  the  juice  of  many  soft, 
succulent  plants  used  for  food  ;  it  may  be  extracted  from 
potatoes  by  macerating  the  sliced  tubers  in  cold  water  con- 
taining a  little  sulphuric  acid. 

564.  Musculine  is  the  name  given  to  the    substance 
which  forms  the  basis  of  muscular  tissue.     This  occurs  in 
FIG  20Q  bundles,  as    shown  in  Fig. 

200,  the  parallel  fibres  hav- 
ing wrinkles  or  cross-mark- 
ings. If  a  piece  of  lean 
beef  be  washed  in  clean  wa- 
ter, its  red  color,  which  is 
due  to  blood,  ffraduallv  dis- 

Fibres  of  Lean  Meat,  magnified.  .          ° 

appears,  leaving  a  whitish 

mass  composed  of  musculine,  and  the  areolar  tissue  which 
binds  the  fibres  of  the  muscle  together.  Like  albumen,  it  is 
capable  of  being  converted  into  an  insoluble  body.  Fibrine 
is  a  constituent  of  blood,  forming  in  the  healthy  state  about 
two  parts  in  1 ,000  parts  of  that  liquid.  The  clotting  of  blood, 
when  freshly  drawn,  is  due  to  the  coagulation  of  its  fibrine, 
which  solidifies  into  a  net-work  of  fibres.  Dilute  solutions 
of  potash  and  soda  dissolve  fibrine,  as  they  do  albumen. 
When  wheat-flour  is  made  into  dough,  and  then  kneaded 
on  a  sieve,  or  a  piece  of  muslin  under  a  stream  of  water, 
its  starch  is  washed  away,  and  there  remains  a  gray,  tough, 
elastic  substance,  almost  resembling  animal  skin  in  appear- 


ALBUMINOUS  SUBSTANCES.  317 

ance.  When  dried  it  has  a  glue-like  aspect,  and  is  there- 
fore called  gluten.  The  crude  gluten  thus  prepared,  when 
freed  from  oil,  albumen,  etc.,  proves  to  be  identical  with 
animal  albumen. 

The  effect  of  boiling  upon  fibrine  is  to  render  it  hard 
and  tough.  Heat,  a£  we  have  seen,  converts  soluble  into 
coagulated  albumen  which  is  insoluble  in  water,  either  hot 
or  cold. 

565.  Caseine  is  an  essential  constituent  of  milk,  exist- 
ing in  it  to  the  extent  of  about  three  per  cent.,  and  form- 
ing its  curd,  or  cheesy  principle.  In  milk  it  is  held  in 
solution  by  the  presence  of  a  small  portion  of  free  alkali, 
and,  when  this  is  neutralized  by  an  acid,  the  caseine  is  pre- 
cipitated, or  the  milk  curdles.  By  neutralizing  the  acid, 
the  caseine  is  redissolved.  Almonds,  peas,  beans,  and 
many  other  seeds,  contain  an  albuminoid  closely  resembling 
caseine,  sometimes  known  as  legumine,  or  vegetable  case- 
ine. This  is  not  coagulable  by  heat,  but  by  alcohol  and 
acetic  acid.  The  coagulated  legumine  resembles  the  curd 
of  milk.  The  Chinese  make  a  cheese  from  peas,  which 
gradually  acquires  the  smell  and  taste  of  milk-cheese. 

Milk  is  a  secretion  of  special  interest  from  the  circum- 
stance that  it  constitutes  the  entire  food  of  the  young  ani- 
mal for  some  months,  and  consequently  must  contain  all 
the  elements  necessary  for  the  rapid  development  of  the 
various  tissues  of  the  body.  It  has  essentially  the  same 
constituents  in  carnivorous  animals  that  it  has  in  the  her- 
bivorous, although  the  proportions  are  somewhat  variable. 
When  examined  under  a  microscope  it  is  seen  to  consist 
of  a  transparent  fluid,  in  which  float  transparent  globules 
consisting  of  fat,  surrounded  by  an  envelope  of  albumen. 
When  milk  is  allowed  to  remain  at  rest  for  a  few  hours,  at 
the  ordinary  temperature  of  the  air,  the  fat-globules  rise 
to  the  surface ;  and,  if  the  layer  of  cream  thus  formed  be 
removed  and  subjected  to  mechanical  action,  the  albumi- 
nous envelope  is  broken,  and  the  globules  of  fat  coalesce 


318  DESCRIVTIVE   CHEMISTRY. 

into  a  mass  forming  butter.  Good  milk,  when  perfectly 
fresh,  is  always  feebly  alkaline ;  when  left  to  itself,  how- 
ever, it  soon  becomes  sour,  and  is  found  to  contain  lactic 
acid.  The  quantity  and  quality  of  milk  vary.  We  give 
below  a  statement  of  the  composition  of  cow's-milk,  from 
an  analysis  made  by  Haidlen  : 

Water 873.00 

Butter       ......  30.00 

Caseine            .....  48.20 

Milk-sugar  .  .  .  .  .43.90 

Calcic  phosphate         ....  2.31 

Magne?ic  phosphate          ....  0.42 

Iron  phosphate            ....  0.07 

Potassic  chloride               ....  1.44 

Sodic  chloride              ....  0.24 

Soda  combined  with  caseine         .                         .  0.42 


1000.00 


566,  Gelatine. — Animal  membranes,  skin,  tendons,  and 
even  bones,  dissolve  in  water  at  a  high  temperature,  more 
or  less  completely,  but  with  very  different  degrees  of  facil- 
ity, giving  solutions  which  on  cooling  acquire  a  soft-solid, 
tremulous  consistence.  The  substance  so  produced  is 
called  gelatine.  It  does  not  preexist  in  the  animal  system, 
but  is  generated  from  the  membranous  tissue  by  the  action 
of  hot  water.  Cut  into  slices  and  exposed  to  a  current  of 
dry  air,  it  shrinks  much  in  volume,  forming  a  transparent, 
glassy,  brittle  mass  soluble  in  hot  water.  The  aqueous  so- 
lution is  precipitated  by  alcohol,  tannin-solution,  and  many 
other  substances.  Gelatine  is  largely  employed  as  an  ar- 
ticle of  food,  and  in  manufactures  as  "  size  "  and  "  glue." 
The  cartilages  of  the  joints,  the  cornea  of  the  eye,  and 
the  ribs,  yield  a  gelatine,  called,  by  way  of  distinction, 
chondrine. 

Chitine,  C9H]2HO6,  constitutes  the  skeletons  of  insects 
and  Crustacea.  It  is  a  white  substance  which  retains  the 


ALBUMINOUS  SUBSTANCES.  319 

form  of  the  texture  from  which  it  is  obtained  ;  the  word 
chitine  means  a  mantle. 

567.  Urea,  CH4ON2,  is  one  of  the  chief  solid  constitu- 
ents of  urine,  from  which  it  may  be  obtained.      It  is  also 
produced  by  heating  ammonic  cyanate  (H4N,CNO),  with 
which   it   is    isomeric.      Urea   crystallizes   in    transparent 
colorless  prisms  soluble  in   water  and  alcohol.     It  is  in- 
odorous, and  has  a  cooling1,  saline  taste.     By  heat  it  is  de- 
composed into  ammonia,  amrnonic  cyanate,  and  C3ranuric 
acid.     This  compound  is  of  special  interest  as  the  first  or- 
ganic compound  artificially  produced. 

568.  Creatine,  C4HnO4Ns. — Creatine  occurs  in  the  juice 
of  flesh.     When  pure,  it  forms  colorless  brilliant  prismatic 
crystals,  readily  soluble  in  hot  water.     The  aqueous  solu- 
tion has  a  slightly  bitter  and  acrid  taste,  and  a  neutral  re- 
action.    It  forms  no  salts  with  acids.     By  the  action  of 
strong  acids,  it  is  converted  into  creatinine. 

569.  Pepsine,  is  a  nitrogenous  substance  contained  in  the 
gastric  juice,  and  has  never  been  perfectly  isolated.  It  is  the 
active  agent  concerned  in  digestion.     An  artificial  gastric 
juice  which  acts  upon  albuminoid  substances  is  obtained 
by  digesting  the  mucous  membrane  of  the  stomach  (usually 
of  a  pig)  with  a  warm,  dilute  solution  of  hydric  chloride. 

570.  Haemoglobins,  also   called  hcemato-crystalline,  is 
made  up  of  carbon,  hydrogen,  iron,  nitrogen,  oxygen,  and 
sulphur,  and  forms  the  chief  part  of  the  red  globules  of  the 
blood  of  vertebrate  animals.      Usually  it   is   amorphous, 
but  from  some  animals  it  can  be  separated  in  crystalline 
form.     Dilute  solutions  of  this  substance  may  be  heated  to 
160°  F.  without  marked  change,  but  if  the  heat  is  continued 
the  haemoglobine  is  disorganized  and  splits  up  into  hmma- 
tine,  CggHj^N^Fe^jg,  and  coagulated  albumen.     Alcohol 
also  decomposes  it. 

571.  Putrefaction. — The  exact  character  of  the  fermen- 
tation which  takes  place  when  animal  bodies  putrefy  is  but 
little  known.    Among  the  products  of  these  changes  are  hy- 


320  DESCRIPTIVE  CHEMISTRY. 

drogen,  nitrogen,  carbonic  dioxide,  ammonia,  hydrogen  car- 
bides, sulphides,  and  phosphides.  The  gaseous  combinations 
of  sulphur  and  phosphorus  are  the  chief  causes  of  the  offen- 
sive odor  of  putrefying  bodies.  As  the  presence  of  moist- 
ure, a  favoring  temperature,  and  access  of  air,  are  essential 
conditions  of  putrefaction,  if  any  of  them  are  withdrawn, 
the  effect  is  prevented.  It  is  well  known  that  the  most 
perishable  organic  substances,  both  vegetable  and  animal, 
may  be  indefinitely  preserved  by  drying.  Cold  checks  de- 
composition, and  it  is  entirely  arrested  by  freezing.  So,  if 
the  prime  inciter  of  change,  the  air  with  its  floating  organic 
germs,  is  excluded,  putrefaction  cannot  take  place.  This 
fact  is  illustrated  by  the  general  practice  of  preserving  all 
kinds  of  alimentary  substances,  meat,  fruits,  and  vegetables, 
in  vessels  which  exclude  the  air.  It  is  not  enough,  how- 
ever, to  exclude  these  agents  from  the  surface  of  ferment- 
able bodies,  the  germs  which  have  already  been  absorbed 
must  also  be  destroyed.  This  may  be  done  by  a  sufficient 
elevation  of  temperature.  In  some  cases  boiling  is  effect- 
ual, in  others  a  much  higher  temperature  is  required. 

572.  Ferment -Diseases.  —  The  foul  accumulations  of 
neglected  towns,  and  the  decomposing  organic  matter  of 
many  swampy  districts,  give  off  invisible  emanations  know7n 
as  miasms  and  malaria,  which  fill  the  air,  and  often  occa- 
sion fatal  epidemics.  Of  their  composition,  nature,  or 
mode  of  action,  nothing  very  definite  is  known,  but  it  has 
been  held  that  the  effects  produced  by  them  are  due  to 
the  presence  of  a  large  quantity  of  ferment-germs  which, 
being  inhaled,  develop  and  induce  a  condition  somewhat 
similar  to  fermentation  in  the  living  system.  Intermittent 
fever,  typhoid  fever,  and  cholera,  have  been  ascribed  to  this 
cause.  Various  other  diseases,  as  small-pox,  hydrophobia, 
etc.,  have  also  with  much  reason  been  considered  as  con- 
sisting in  processes  of  fermentation  running  their  course 
in  the  living  organism. 


APPENDIX. 


The  Metrical  System  of  Weights  and  Measures. 

LENGTH. 

Kilometre =  1000  metres. 

Hectometre =  100      " 

Decametre =  10      " 

METRE  (m.) =  1    metre. 

Decimetre =  0.1     " 

Centimetre  (cm.) =  0.01  u 

Millimetre  (mm.) =  0.001" 

VOLUME. 

Kilolitre =1000    litres. 

Hectolitre =  100       " 

Decalitre =  10      " 

LITRE =  1     litre. 

Decilitre =  0.1      " 

Centilitre =  0.01    " 

Millilitre  (or  cubic  centimetre)  (c.  c.) =  0.001  " 

WEIGHT. 

Kilogramme =  1000  grammes. 

Hectogramme =  100 

Decagramme —  10 

GRAMME  (grm.) =  1  gramme. 

Decigramme =  0.1 

Centigramme =  0.01    " 

Milligramme =  0.001" 


The  metre =  39.368  inches. 

The  litre =    1.76  pints. 

The  gramme =  15.432  grains, 


323 


APPENDIX. 


Relation  of  the  Scales  of  the  Centigrade  and  Fahrenheit 
Thermometers. 


Cent. 

Fahr. 

Cent. 

Fahr.      Cent. 

Fahr. 

Cent. 

Fahr. 

+  100  = 

+  212 

+  64  = 

+  147.2 

4-  29  = 

+  84.2 

—  6  = 

=  +  21.2 

99  = 

210.2 

63  = 

145.4 

28  = 

82.4 

7  = 

19.4 

98  = 

208.4 

62  = 

143.6 

27  = 

80.6 

8  = 

17.6 

97  = 

206.6 

61  = 

141.8 

26  = 

78.8 

9  = 

15.8 

96  = 

204.8 

60  = 

140 

25  = 

77 

10  = 

14 

95  = 

203 

59  = 

138.2 

24  = 

75.2 

11  = 

12.2 

94  = 

201.2 

58  = 

136.4 

23  = 

73.4 

12  = 

104 

93  --= 

199.4 

57  = 

134.6 

22  = 

71.6 

13  = 

8.6 

92  = 

197.6 

56  = 

132.8  ! 

21  = 

69.8 

14  = 

6.8 

91  = 

195.8 

55  = 

131 

20  = 

68 

15  = 

5 

90  = 

194 

54  = 

129.2 

19  = 

66.2 

16  = 

3.2 

89  = 

192.2 

53  = 

127.4 

18  = 

644 

17  = 

1.4 

88  = 

190.4 

52  = 

125.6 

17  = 

62.6 

18  = 

=  —  0.4 

8T  = 

188.6 

51.= 

123.8 

16  = 

60.8 

19  = 

2.2 

86  = 

186.8 

50  = 

122 

15  = 

59 

20  = 

4 

85  = 

185 

49  = 

120.2 

14  = 

57.2 

21  = 

5.8 

84  = 

188.2 

48  = 

118.4  ! 

13  = 

55.4 

22  = 

7.6 

83  = 

181.4 

47  = 

116.6  | 

12  = 

53.6 

23  = 

9.4 

82  = 

179.6 

46  = 

114.3  ! 

11  = 

51.8 

24  = 

11.2 

81  = 

177.8 

45  = 

118 

10  = 

50 

25  = 

13 

80  = 

176 

44  = 

111.2  i 

9  = 

48.2 

26  = 

:     14.8 

79  = 

174.2 

43  = 

109.4  | 

8  = 

46.4 

27  = 

16.6 

78  = 

172.4 

42  = 

107.6  '     7  = 

44.6 

28  = 

18.4 

77  = 

170.6 

41  = 

105.8  ! 

6  = 

42.8 

29  = 

20.2 

76  = 

163.8 

40  = 

104 

5  = 

41 

30  -  = 

22 

75  = 

167 

39  = 

102.2 

4  = 

39.2 

31  = 

23.8 

74  = 

165.2 

83  = 

103.4 

3  = 

37.4 

82  = 

25.6 

73  = 

163.4 

37  = 

9S.6 

2  = 

85.6 

33  = 

27.4 

72  = 

161.6 

36  = 

96.8 

-I   

33.8 

34  = 

29.2 

71  = 

159.8 

35  = 

95 

0  = 

32 

35  = 

81 

70  = 

158 

34  = 

932 

—  1  = 

80.2 

36  = 

32.8 

69  = 

156.2 

83  = 

91.4 

2  = 

28.4 

37  = 

34.6 

68  = 

154.4 

82  = 

89.6 

3  = 

26.6 

38  = 

86.4 

67  = 

152.6 

31  = 

87.8 

4  = 

24.3 

39  r 

88.2 

66  = 

150.8 

80  = 

86 

5  = 

23 

40  = 

40 

65  = 

149 

It  is  often  necessary  to  convert  temperatures  expressed  on  the  Fahren- 
heit scale  into  the  corresponding  temperatures  on  the  Centigrade  scale, 
and  the  following  rules  will  assist  the  pupil  in  transforming  one  scale 
into  the  other : 

(1.)  To  convert  Fahrenheit  Degrees  into  Centigrade  Degrees. — Subtract 
32  from  the  number  of  degrees,  and  multiply  the  remainder  by  f  (or  0.5). 

(2.)  To  convert  Centigrade  Degrees  into  Fahrenheit  Degrees. — Multiply 
the  number  of  degrees  by  g  (or  1.8),  and  add  32  to  the  product. 


APPENDIX. 


323 


Table  for  the  Conversion  of  Grammes  into  Grains ,  Cen- 
timetres into  Inches,  and  Litres  into  Quarts. 


CONVERSION. 

1. 

2. 

3. 

4. 

5. 

Grammes  into  Grains  

15.4346 

80.8692 

46.3038 

61.7384 

77.1730 

Centimetres  into  Inches  

.3937079 

.7374153 

1.1811237 

1.574S316 

1.9685395 

Litres  into  Imperial  Quarts.. 

O.SS066 

1.761:32 

2.64193 

3.52264 

4.40330 

Litres  into  U.  8.  Quarts  

1.05708 

2.11415 

3.17123 

4.22830 

5.2SSa3 

Table  of  Elementary  Atoms  and  Molecules. 


NAMES  OF 
PERISSAD  ELEMENTS. 

Symbols  of 
Atoms. 

11 

ll 

Quantivalence. 

Atomic 
Weight. 

Hydrogen  

H 

li-H 

1. 

1.0 

Fluorine  

Fl 

F-F 

I. 

19.0 

Chlorine  

Cl 

Cl-Cl 

I..  III.,  V.,  VII. 

35.5 

Bromine 

Br 

Br-Br 

I.  III.  V.,  VII. 

80.0 

Iodine  

I 

I-I 

L,  IIL,  V.,  VII. 

127.0 

Lithium 

Li 

Li-Li 

I. 

70 

Sodium  (Natrium)  

Na 

Na-Na 

I.,  III. 

23.0 

Potassium  (Kalium)  
Rubidium  . 

K 

Rb 

K-K 
Rb-Kb 

I.,  III.,  V. 
I. 

39.1 
85.4 

Caesium  

Cs 

Cs-Cs 

I. 

133.0 

Silver  (Argentum)  

Ag 

Ag-Ag? 

I.,  III. 

103.0 

Thallium  

Tl 

T1-T1  ? 

I.,  III. 

204.0 

Gold  (Auruni)  

Au 

Au=Au? 

I..  III. 

197.0 

Boron  

B 

B=B? 

III. 

11.0 

Nitrogen 

N 

N=N 

I.,  III.,  V. 

14.0 

Phosphorus  

P 

I..  III.,  V. 

81.C 

As 

I  ,  III.  V. 

750 

Antimony  (Stibium)  
Bismuth  

Sb 
Bi 

2? 
? 

III.,  V. 
III.,  V. 

122.0 
210.C 

Vanadium  

Va 

V=V? 

III.,  V. 

51.37 

Uranium  

TTr 

UiU? 

III.,  V. 

120.0 

Columhium  

Cb 

CbiCb? 

V. 

94.0 

Tantalum        

Ta 

TafTa? 

V. 

1820 

324 


APPENDIX, 


NAMES  OF 
ARTIAD  ELEMENTS. 

Symbols  of 
Atoms. 

8 

Ej 

ooS 

Quantivalence. 

Atomic 
Weight. 

Oxygen  

O 

OO 

II. 

16.0 

Sulphur. 

s 

8=8 

II    IV    VI 

32  0 

Selenium  
Tellurium  

Se 
Te 

Se=Se 
To=Te 

II.,  IV.,  VI. 
II.,  IV.,  VI. 

79.4 
128.0 

Molybdenum  
Tungsten  (  Wolfram)  

Mo 
W 

Mo? 
W? 

II.,  IV.,  VI. 
IV.,  VI. 

96.0 
184.0 

Copper  (Cuprum)  
Mercury  (Hydrargyrum)  . 

Cu 
Hg 

Cu? 
Hg 

II. 
II. 

63.4 
200.0 

Calcium  . 

Ca 

Ca? 

II. 

40  0 

Strontium  

Sr 

Sr? 

ii.,  rv. 

87.6 

Barium  

Ba 

Ba? 

ii. 

137  0 

Lead  (Plumbum)  

Pb 

Pb? 

II.,  IV. 

207.0 

Magnesium 

Mg 

Mg? 

ii 

24  0 

Zinc  

Zn 

Zn? 

ii. 

66.2 

Indium  . 

In 

In  9 

II    IV    VI 

72  0 

Cadmium  

Cd 

Cd 

II.' 

112.0 

Glucinum  

G 

G? 

II. 

9.8 

Yttrium  

Y 

Y? 

II. 

61.7 

Erbium  

E 

E? 

II. 

112.6 

Cereum  .  .  . 

Ce 

Ce? 

11.  IV 

92  0 

Lanthanum 

La 

La? 

II 

98  6 

Didymium  

D 

D? 

II. 

95.0 

Nickel  .  . 

Nl 

Ni? 

II.,  IV. 

58.8 

Cobalt  

Co 

Co? 

II.,  IV. 

58.8 

Manganese  
Iron  (Ferrum)  

Mn 
Fe 

Mn? 
Fe? 

II.,  IV.,  VI. 
II.,  IV.,  VI. 

55.0 
56.0 

Chromium  

Cr 

Cr? 

II.,  IV    VI 

52  2 

Aluminium     

Al 

Al? 

IV. 

27.4 

Ruthenium  
Osmium  

Ku 
Os 

Eu? 
Os? 

II.,  IV.,  VI. 
11.,  IV.,  VI. 

104.4 
199.2 

Rhodium  .  . 

Eo 

Eo? 

II    IV    VI 

104  4 

Iridium  

Ir 

Ir? 

II..  IV.,  VI. 

196.0 

Palladium 

Pd 

Pd? 

II    IV 

106  6 

Platinum  

Pt 

Pt? 

II.,  IV. 

197.4 

Titanium 

Ti 

Ti  ' 

II    IV 

50  0 

Tin  (Stannum)  

Sn 

Sn? 

II.,  IV. 

118.0 

Zirconium  

Zr 

Zr? 

IV. 

89.6 

Thorium  

Th 

Th? 

II. 

115.72 

Silicon  

Si 

Si? 

IV. 

28.0 

Carbon 

c 

C? 

II  ,  IV. 

12.0 

NOTE  TO  PAGE  91. 

The  views  presented  in  the  text  concerning  the  distribution  of  the 
spectrum  forces  have  long  been  regarded  as  established.  But  Dr.  J.  W. 
Draper  maintains  that,  while  the  effects  described  are  true  as  matters  of 
observation,  they  are  variously  interpreted.  He  says  that  the  accumula- 


APPENDIX.  325 

tion  of  heat  at  one  end  of  the  spectrum  is  due  to  the  same  cause  as  the 
unequal  spaces  of  the  colors — that  is,  to  the  distorting  action  of  the 
prism.  With  a  diffraction  spectrum  produced  by  finely-ruled  surfaces, 
he  claims  to  have  found,  by  many  experiments,  that  the  luminous  spaces 
are  equal ;  that,  from  the  centre  of  the  spectrum,  near  the  sodium-line  D, 
there  are  equal  amounts  of  heat  on  the  two  sides  ;  and,  finally,  that  all 
the  rings  of  the  spectrum,  irrespective  of  their  color  or  wave-length,  have 
equal  heating-power. 


QUESTIONS. 


INTRODUCTION. 

1.  WHAT  is  meant  by  the  terms  phenomena  and  order  of  Nature  ? 
2.  What  purpose  does  prevision  serve  in  science  ?  3.  Define  matter  and 
force.  4.  What  are  physical  changes  ?  5.  Give  examples  of  chemical 
changes  of  matter.  Give  the  distinction  between  compound  and  sim- 
ple bodies.  6.  Are  the  forces  of  Nature  in  any  way  connected  ? 


CHAPTER  I.— GRAVITY. 

7.  SHOW  how  the  processes  of  weighing  and  measuring  are  impor- 
tant to  the  chemist.  What  system  of  measurement  is  now  in  ordinary 
use?  What  is  the  metrical  scale?  8.  What  is  its  basis  ?  Describe  this 
scale  fully.  9.  What  is  gravity  ?  Give  illustration  showing  mutual  at- 
traction of  masses  of  matter.  What  relation  exists  between  the  quan- 
tity of  matter  and  the  force  of  gravity?  10.  What  is  weight?  11.  De- 
scribe the  balance.  12.  In  what  does  the  operation  of  weighing  con- 
sist? 13.  Give  the  unit  of  the  French  scale  of  weights.  The  gramme 
is  equal  to  how  many  grains  ?  14.  How  may  specific  volumes  be  ob- 
tained? 15.  How  is  volume  related  to  weight?  How  is  platinum  re- 
lated to  hydrogen  ?  What  is  specific  gravity?  16.  How  is  the  specific 
gravity  of  solids  heavier  than  water  obtained?  17.  How  is  the  specific 
gravity  of  solids  lighter  than  water  obtained  ?  18.  What  precaution 
should  be  taken  in  finding  the  specific  gravity  of  powdered  solids  ?  19. 
How  may  the  specific  gravity  of  soluble  solids  be  obtained  ?  20.  How 
may  the  specific  gravity  of  gases  be  obtained  ?  21.  Explain  the  prin- 
ciple on  which  the  hydrometer  is  constructed.  22.  How  does  specific 
gravity  afford  means  of  identifying  bodies  ?  23.  Give  distinction  between 
specific  gravity  and  density. 


QUESTIONS.  327 

CHAPTER   II.— MOLECULAR  ATTRACTIONS. 

25.  WHAT  reason  can  be  given  for  the  conclusion  that  matter  is 
universally  porous  ?  27.  What  are  atoms  ?  How  are  they  distinguished 
from  molecules  ?  28.  State  what  you  can  of  the  divisibility  of  matter  ? 
29.  Give  distinction  between  adhesion  and  cohesion.  31.  Explain  con- 
ditions of  "  wetting."  32.  What  is  capillary  attraction  ?  33.  What  is 
said  of  reversed  capillarity  ?  34.  How  may  a  gas  be  driven  out  from 
a  solution  ?  35.  How  may  insects  walk  upon  water  ?  36.  Explain 
what  takes  place  in  diffusion.  37.  What  principle  explains  the 
stability  of  our  atmosphere?  38.  What  is  the  law  of  the  diffusion 
of  gases?  39.  What  is  osmose?  Explain  Fig.  14.  What  occurs  in 
atmospheric  respiration?  40.  May  liquids  and  solids  diffuse  through 
gases?  42.  What  are  diffusates?  What  are  crystalloids  and  colloids? 
43.  Explain  endosmose  and  exosmose.  44.  What  is  the  difference  be- 
tween absorption  and  osmose?  45.  What  is  meant  by  the  terms  solu- 
tion and  solvent  ?  46.  What  conditions  favor  solution  ?  47.  When 
is  a  liquid  saturated  ?  48.  How  may  solids  be  separated  from  solution  ? 
Give  examples.  50.  What  is  occlusion?  51.  What  are  crystals? 
What  are  substances  called  which  do  not  crystallize?  53.  How  may 
crystals  be  artificially  produced  ?  54.  What  is  mother-liquor  ?  55. 
What  is  said  of  crystals  by  fusion  ?  57.  Does  crystallization  ever  take 
place  except  in  liquids  ?  58.  State  phenomena  attending  crystallization  ? 
61.  What  forms  do  liquids  tend  to  assume  on  crystallizing?  62.  Crystals 
are  solids  of  what  class  ?  63.  What  are  primary  forms  ?  What  is  a 
goniometer  ?  64.  How  many  systems  of  crystallization  are  there  ?  65. 
Describe  the  monometric  system.  66.  How  are  the  axes  arranged  in  the 
dimetric  system?  67.  Give  examples  of,  and  describe,  the  trimetric 
system.  69.  Give  characteristics  of  rhombohedral  and  hexagonal  sys- 
tems. 71.  What  evidence  is  there  that  the  axes  of  crystals  are  not 
mere  imaginary  lines  ?  72.  What  is  cleavage  ?  73.  What  example  of 
the  derivation  of  form  is  given  ?  74.  What  is  isomorphism  ?  75.  What 
is  dimorphism  ? 

CHAPTER  III.— HEAT. 

76.  GIVE  the  term  which  is  applied  to  the  science  of  heat.  77. 
What  is  the  general  effect  of  heat  upon  matter  ?  78.  How  may  the  cohe- 
sion of  a  solid  be  overcome  ?  79.  May  gases  be  expanded  indefinitely  ? 
80.  What  do  thermometers  measure  ?  81.  What  advantages  has  mer- 
cury as  a  thermometric  fluid  ?  82.  Give  the  different  thermometers  in 
use,  and  state  the  peculiarity  of  each.  83.  How  is  heat  transferred  ? 
What  are  the  best  conductors  ?  84.  Does  heat  travel  with  more  facil- 


328  QUESTIONS. 

ity  across  the  axis  than  in  other  directions  ?  85.  Why  do  some  sub- 
stances feel  so  much  warmer  than  others  ?  86.  Explain  what  takes  place 
when  gases  and  liquids  are  heated.  87.  What  is  radiation  ?  How  may 
equilibrium  of  temperature  be  obtained  ?  88.  What  effect  does  surface 
have  on  radiation  ?  89.  What  substances  are  good  absorbers  of  heat  ? 
90.  What  is  dew  ?  91.  What  two  kinds  of  radiant  heat  are  there  ?  92 
Define  the  terms  diathermic  and  athermic.  93.  How  does  the  aqueous 
vapor  affect  the  temperature  of  the  earth  ?  94.  What  is  the  melting- 
point  of  a  substance  ?  95.  Give  the  distinction  between  latent  heat 
and  sensible  heat.  96.  What  is  sensible  heat  ?  97.  Explain  how  freez- 
ing is  a  warming  process.  98.  What  is  a  freezing  mixture  ?  99.  Ex- 
plain the  process  called  "  boiling."  100.  What  circumstances  affect  the 
boiling-point?  101.  What  is  the  spheroidal  state?  102.  What  sub- 
stances vaporize  readily  ?  103.  What  becomes  of  the  heat  which  has 
been  consumed  in  converting  liquids  into  vapors  ?  104.  On  reversing 
the  process  what  occurs  ?  105.  What  is  the  effect  of  evaporation  ? 
106.  Explain  the  cryophorus.  107.  How  can  the  amount  of  atmospheric 
humidity  be  obtained  ?  108.  Explain  the  hygrometer.  109.  What  re- 
lation is  there  between  the  vapor  from  a  cubic  inch  of  water,  one  of 
alcohol,  and  one  of  ether  ?  110.  What  is  meant  by  elastic  force?  111. 
Explain  distillation,  and  give  the  meaning  of  the  terms  distillate  and 
sublimate.  112.  How  may  gases  be  reduced  to  liquid  or  solid  condi- 
tions? 114.  What  is  the  difference  between  heat  and  cold?  115. 
Give  an  idea  of  the  caloric  hypothesis.  116.  Give  the  facts  which 
led  to  the  new  theory.  117.  Heat  is  now  how  regarded  ?  What  is  sup- 
posed to  be  true  of  the  atoms?  118.  What  follows  from  this  theory 
with  regard  to  the  temperature  of  bodies  ?  119.  What  is  the  dynamical 
theory?  120.  What  is  combustion  ? 

CHAPTER  IV. — ELECTRICITY. 

121.  STATE  what  is  said  of  electricity?  122.  What  are  conductors 
and  insulators ?  123.  How  do  the  electricities  affect  each  other?  124. 
Explain  the  terms  "charged"  and  "discharged."  125.  What  is  the 
effect  of  bringing  an  excited  glass  tube  near  an  electroscope  ?  What  is 
electrical  induction?  126.  Explain  Fig.  48.  127.  State  Faraday's  theory 
of  induction.  128.  What  is  a  natural  magnet?  129.  What  is  the  law 
of  polarity?  130.  Explain  the  term  magnetic  induction  by  reference 
to  the  figure.  131.  What  is  the  result  of  breaking  a  magnet?  132. 
What  are  those  substances,  which  arrange  themselves  axially,  called? 
133.  What  is  voltaic  electricity,  and  whence  the  name?  Describe  the 
voltaic  circuit.  134.  What  are  the  poles  of  the  circuit?  135.  How 
may  the  power  of  the  circuit  be  increased?  136.  How  may  increased 


QUESTIONS.  329 

effect,  combined  with  steadiness  of  action,  be  secured  ?  137.  Describe 
DanielFs  battery.  138.  Upon  what  does  quantity  of  electricity  depend? 
139.  Explain  the  principle  of  the  Ruhmkorff  coil.  140.  Will  voltaic 
electricity  travel  through  air ?  141.  What  is  electrolysis?  142.  Which 
bodies  are  termed  electro-negative,  which  electro-positive?  143.  Explain 
electro-gilding  and  electro-plating.  144,  What  relation  exists  between 
arrested  electricity  and  heat?  145.  Upon  what  do  the  degree  and 
direction  of  the  motion  of  the  needle  depend  ?  146.  What  is  the  astatic 
needle  ?  147.  What  is  thermo-electricity  ? 

CHAPTER  V.— LIGHT. 

149.  STATE  what  you  can  of  light;  give  its  velocity.  150.  How  is 
light  affected  by  the  prism?  What  is  the  order  of  refrangibility  of 
the  rays?  151.  Give  the  wave-hypothesis.  152.  What  to  the  eye  is  the 
same  as  the  gamut  to  the  ear  ?  How  do  the  number  of  waves  of  red 
light  compare  with  those  of  blue  light  in  a  given  space?  153.  What 
explanation  is  given  of  radiant  heat?  154.  What  is  interference? 
155.  Explain  Fig.  70.  The  principle  of  interference  leads  to  what  con- 
clusions regarding  silence,  darkness,  etc.  ?  1 56.  What  happens  when 
light  is  reflected  at  a  certain  angle  ?  How  may  the  change  be  detected  ? 
157.  In  what  other  ways  may  light  be  polarized?  158.  Show  how  the 
wave-theory  explains  polarization. 

CHAPTER   VI.— CHEMISTRY  OF  LIGHT. 

162.  UPON  what  rays  does  the  art  of  photography  depend?  163. 
Describe  Fig.  87,  and  state  the  facts  regarding  invisible  radiations. 
164.  How  do  heat-rays,  light-rays,  and  chemical  rays,  differ  from  each 
other?  165.  What  are  actinoroeters ?  166.  What  changes  take  place 
in  the  chemical  activity  of  the  solar  rays,  at  different  times  of  the  day 
and  year?  167.  What  is  said  of  chemical  action  at  the  equator?  168. 
Where  does  the  force  which  is  most  active  in  vegetative  processes 
reside?  169.  State  the  chemical  effects  of  light?  170.  What  chemi- 
cals are  employed  in  photography?  171.  State  how  the  invisible  image 
is  produced.  172.  How  is  the  invisible  image  brought  out?  173. 
What  are  negatives  and  positives  ?  174.  Give  some  idea  of  the  varying 
effects  of  colored  lights.  175.  How  is  photography,  in  its  applications, 
related  to  science  ? 

CHAPTER  VII. — SPECTRUM  ANALYSIS. 

176.  How  is  spectrum  analysis  related  to  other  modern  discov- 
eries? 177.  What  is  proved  by  recombining,  by  means  of  a  lens,  the 


330  QUESTIONS. 

separated  colored  rays?  178.  May  the  colors  of  the  solar  spectrum  be 
still  further  decomposed?  179.  What  is  said  of  the  spectrum  of  the 
electric  light?  180.  What  is  dispersion?  How  does  the  dispersive 
power  of  flint-glass  compare  with  that  of  crown-glass  ?  181.  How  may 
dispersion  be  increased?  182.  When  may  four  or  five  prisms  be  used 
to  advantage  ?  183.  Describe  the  spectroscope,  and  explain  Figs.  100, 
101,  and  102.  187.  What  was  Dr.  Wollaston's  discovery?  188. 
State  what  is  said  of  Fraunhofer's  lines.  189.  Give  the  results  of  Dr. 
Draper's  investigations.  ,190.  How  do  the  spectra  of  gaseous  bodies 
differ  from  those  of  solids  ?  What  is  the  difference  in  the  spectra  of 
sodium  and  iron?  191.  These  spectral  lines  may  serve  as  tests  for 
what  ?  192.  Increasing  temperature  and  added  pressure  have  what 
effect  on  the  spectrum?  193.  What  are  the  spectrum-lines?  194. 
What  relation  exists  between  the  dark  solar  lines  and  the  bright  lines 
produced  by  burning  terrestrial  substances  ?  195.  What  are  absorption- 
lines  ?  196  What  kind  of  light  do  vapors  absorb  ?  Explain  Fig.  109. 

197.  What  is  meant  by  the  reversal  of  the  lines?     Describe  Fig.  110. 

198.  What  principle  of  physics  underlies  the  theory  upon  which  spec- 
trum analysis  is   based?     199.    What  clew  is   given   us   by  Fraunhof- 
er's  lines  ?     200.    Give  illustrations  showing  the  delicacy  of  spectrum 
analysis,  when  used  as  a  means  of  testing  chemical  substances.     201. 
Mention  the  names   of  the   new   elements    discovered   by  this   means. 
202.  Explain  use  of  spectroscope  in  steel-making.     203.  Give  organic 
indications  of  the  spectroscope.      204.  Give  description  of  telespeotro- 
scope.     205.  How  does  Prof.  Young  describe   the  red  portion  of  the 
spectrum  ?     206.  Describe  the  solar  envelope.     207.  What  elements  are 
found  in  the  sun  ?     208.  What  evidence  does  spectrum  analysis  give  us 
that  stars  are  suns?     211.  Give  the  spectroscopic  proof  of  the  motions 
of  celestial  bodies.     212.  How  does  spectrum  analysis  prove  the  motions 
of  the  stars. 


CHAPTER  VIII. — GENERAL  CHARACTER  OF  CHEMICAL  ACTION. 

GIVE  a  general  idea  of  chemical  force.  216.  Define  analysis,  prox- 
imate, ultimate,  qualitative,  and  quantitative.  217.  How  do  the  effects 
of  chemical  force  differ  from  those  of  the  physical  forces?  218.  Why 
are  some  substances  called  elements,  and  others  compounds  ?  220. 
How  is  chemical  action  affected  by  cohesion,  heat,  light,  and  electricity ! 
223.  What  is  chemical  induction  ?  224.  When  will  nitrogen  and  hydro- 
gen unite  to  form  ammonia  ?  225.  Define  catalysis.  226.  Is  there  any 
variation  in  the  intensity  of  chemical  action  ?  227.  Has  chemistry  any 
mathematical  basis?  228.  Give  the  principle  underlying  the  law  of 


QUESTIONS.  331 

definitive  proportions.      229.  Explain  the  law  of  multiple  proportions. 
230.  Give  example  of  equivalent  proportion. 

CHAPTER   IX.— THEORETICAL  CHEMISTRY. 

231.  GIVE  an  idea  of  the  old  atomic  theory,  and  of  the  theory  as 
revived  by  Dr.  Dalton.  233.  Define  the  term  molecule  as  used  by  the 
physicist.  234.  Define  the  term  molecule  as  used  by  the  chemist.  235. 
What  is  the  ultimate  unit  of  the  chemist  called  ?  Define  the  terms  anal- 
ysis, synthesis,  and  metathesis.  236.  What  quantity  of  an  element  does 
the  symbol  represent  ? 

237.  What  theory  was  first  given  in  explanation  of  chemical  changes  ? 
238.  Give  a  general  idea  of  the  binary  theory.  239.  What  theory 
was  the  outgrowth  of  the  binary  theory?  240.  Give  a  statement  of 
the  theory  of  types.  241.  Do  substitutions  take  place,  atom  for  atom  ? 
242.  Define  the  term  atomicity,  and  give  groupings  illustrating  the 
subject.  243.  What  is  quantivalence ?  How  is  it  expressed?  244. 
What  is  the  significance  of  bonds  ?  245.  What  relation  exists  between 
the  number  of  bonds  and  the  ability  of  the  atoms  to  combine  with 
each  other  ?  246.  To  what  is  the  term  atomicity  limited  ?  247.  Define 
terms  perissad  and  artiad.  May  a  perissad  ever  become  an  artiad? 
248.  How  is  it  supposed  that  changes  of  quantivalence  may  be  ex- 
plained ?  249.  When  may  an  atom  or  molecule  exist  free  ?  Does  the 
quantivalence  of  a  molecule  depend  upon  the  atomicity  of  its  elements  ? 
251.  How  may  molecular  chains  be  formed?  252.  What  are  radi- 
cals? 253.  Define  compound  radicals.  254.  Can  compound  radicals 
exist  free?  255.  On  what  theory  were  acids,  bases,  and  salts,  for- 
merly explained  ?  256.  What  is  the  relation  of  water  to  the  acids  and 
bases  ?  257.  Give  the  constitution  of  the  acids.  258.  What  is  the  con- 
stitution of  a  base?  259.  Give  formulas  for  acids,  bases,  and  salts. 
260.  What  are  hydrates?  261.  Is  hydrogen  an  essential  constituent  of 
acids,  bases,  and  salts?  262.  What  are  ortho-acids  and  meta-acids? 
263.  What  are  normal  salts  ?  264.  Is  common  salt  properly  a  salt  ? 
265.  Explain  the  constitution  of  the  amides,  amines,  and  alkalamides? 

267.  Show  how  the   modern   ideas   of  changes  by  substitution,  types, 
atomicity,  etc.,  are  the  result  of  investigations  in   organic   chemistry. 

268.  What  are  the  important  organic  elements  ?     268.  What  is  the  rela- 
tion of  carbon  to  organic  chemistry  ?    269.  How  are  isomeric  phenomena 
explained?     270.    When  are  compounds  said  to   be   polymeric?     271. 
Define  allotropism.      272.  Are  molecules  to  be  regarded  as  having  di- 
mensions?    273.  What  is  the  law  of  Avogadro?     274.  What  conclusion 
has  been  reached  regarding  the  diameters  of  gaseous  molecules  ?     275. 
Explain  how  the  molecular  weight  of  all  aeriform  bodies  may  be  deter- 


332  QUESTIONS. 

mined.  276.  What  is  the  standard  of  molecular  weight  ?  What  is  the 
crith  ?  277.  How  is  atomic  heat  related  to  specific  heat  ?  278.  In  what 
ratios  do  gases  combine  by  volume  ? 

CHAPTER  X. — THE  CHEMICAL  NOMENCLATURE. 

280.  SHOW  how  the  science  of  chemistry  is  reflected  in  the  language. 
281.  How  have  the  elements  generally  been  named?  What  is  the  sig- 
nificance of  the  terminations  um  and  ine?  282.  What  termination  is 
given  to  the  compound  radicals  ?  283.  In  the  naming  of  binary  com- 
pounds which  element  is  placed  first  ?  What  change  takes  place  in  the 
termination  of  the  positive  element?  What  significance  have  the  pre- 
fixes hypo  and  per  ?  284.  Illustrate  the  use  of  numerical  prefixes.  285. 
How  are  acids  named  ?  How  salts  ?  How  bases  ?  286.  Give  examples 
of  the  names  of  amides,  amines,  and  alkalamides?  287.  Define  em- 
pirical formula  and  rational  formula.  How  are  atomic  groups  sepa- 
rated ?  288.  In  what  form  may  chemical  reactions  be  expressed  ? 

CHAPTER  XI. — HYDROGEN 

289.  WHAT  are  the  quantivalence  and  atomic  weight  of  hydrogen  ? 
290.  What  is  the  significance  of  the  term  hydrogen?  291.  To  what  ex- 
tent is  hydrogen  found  in  Nature?  292.  In  what  different  ways  may- 
hydrogen  gas  be  obtained?  293.  Describe  a  pneumatic  trough.  294. 
Give  properties  of  hydrogen.  296.  How  does  hydrogen  compare  with 
other  elements  in  weight  ?  296.  What  is  known  of  its  inflammability 
and  explosiveness  ?  297.  How  may  hydrogen  be  ignited  without  the  ap- 
plication of  heat  ?  298.  What  is  occlusion  ? 

CHAPTER  XII.— CHLORINE,  FLUORINE,  BROMINE,  IODINE. 

299.  WHERE  is  chlorine  chiefly  found?  300.  How  is  the  gas  ob- 
tained? 301.  What  are  the  properties  of  chlorine?  302.  Its  uses? 
How  does  chlorine  act  as  a  bleaching  agent  ?  303.  What  is  the  composition 
of  muriatic  acid  ?  Give  the  reaction  which  takes  place  when  sulphuric  acid 
acts  on  sodic  chloride.  305.  How  may  chlorine  combine  with  oxygen  ? 
306.  What  use  is  made  of  chloric  monoxide?  308.  What  are  the 
properties  of  chloric  acid  ?  309.  Is  fluorine  found  uncombined  in  Na- 
ture? 310.  What  is  the  distinguishing  characteristic  of  hydric  fluo- 
ride? 311.  How  is  bromine  obtained?  312.  Give  properties  and  uses 
of  bisemine.  313.  What  does  the  term  iodine  refer  to  ?  314.  What  is 
the  test  for  iodine?  For  what  is  iodine  used?  315.  When  bromine 
and  iodine  are  heated  with  hydrogen,  what  compounds  are  formed  ?  ?16. 
What  «an  you  say  of  the  halogen  group  ? 


QUESTIONS.  333 

CHAPTER  Xin. — SODIUM,  POTASSIUM,  LITHIUM,  RUBIDIUM,  CAESIUM. 

317.  WHAT  was  the  first  method  of  obtaining  metallic  sodium? 
318.  What  is  the  chemical  name  of  common  salt?  From  what  source  is 
salt  chiefly  obtained  ?  320.  Give  uses  of  common  salt.  321.  How  are 
sodic  compounds  distinguished  from  potassic  compounds  ?  What  is  the 
composition  of  sodic  carbonate?  322.  Give  common  name  of  hydro- 
sodic  carbonate.  323.  How  is  caustic  soda  obtained?  324.  What  is 
the  chemical  name  for  Glauber's  salt  ?  325.  Give  symbol  of  sodic  ni- 
trate. 326.  How  was  potassium  first  obtained?  327.  What  takes 
place  when  potassium  is  thrown  upon  water  ?  Why  is  this  metal  kept 
in  naphtha?  329.  Give  the  properties  of  potassic  hydrate.  331. 
Where  are  the  potassic  salts  found  ?  What  use  has  potassic  carbonate  ? 
332.  How  may  hydro-potassic  carbonate  be  formed  ?  333.  Give  common 
name  for  potassic  nitrate.  What  is  it  used  for  ?  334.  Give  composition 
of  gunpowder.  335.  What  use  has  potassic  chlorate  in  the  laboratory  ? 
336.  What  is  soluble  glass  ?  337.  Describe  the  process  of  soap-making. 
Upon  what  does  the  consistence  of  the  soap  depend  ?  338.  How  does 
soap  act  in  cleansing  ?  339.  What  elements  are  found  associated  with 
sodium  and  potassium  ?  Where  is  rubidium  found  ?  What  does  the 
word  caesium  mean  ? 

CHAPTER  XIV.— SILVER,  GOLD,  BORON. 

340.  WHAT  is  silver  associated  with  ?  341.  Give  its  properties  and 
uses.  342.  What  is  the  common  name  of  argentic  chloride?  344. 
Give  composition  of  lunar  caustic.  How  may  the  stains  of  indelible 
ink  be  removed  ?  345.  What  is  the  method  employed  to  separate  gold 
from  its  ores  ?  346.  How  does  gold  compare  with  other  metals  in 
malleability  and  ductility  ?  What  is  aqua  regia  ?  347.  What  does  one 
modification  of  boron  resemble  ?  348.  Where  is  boric  acid  found  ?  349. 
What  is  borax  ?  What  property  renders  borax  a  valuable  reagent  ? 

CHAPTER  XV.— NITROGEN,  PHOSPHORUS,  ARSENIC,  ANTIMONY,  BISMUTH. 

350.  How  is  nitrogen  obtained  ?  352.  For  what  is  nitrogen  re- 
markable ?  353.  Give  the  composition  and  method  of  obtaining  am- 
monia. 354.  Why  was  it  called  spirits  of  hartshorn  ?  356.  Nitrogen 
combines  with  oxygen  forming  what  compounds  ?  357.  What  is  laugh- 
ing gas  ?  358.  What  effect  is  produced  on  the  nervous  system  by  nitric 
monoxide  ?  359.  Give  composition  of  nitric  acid.  360.  Its  properties 
and  uses.  362.  When  hydric  chloride  and  ammonia  are  brought  together, 
what  substance  is  formed  ?  Give  the  equation  which  expresses  the  reac- 
tion when  ammonic  chloride  is  formed.  363.  How  is  ammonic  hydrate 


334  QUESTIONS. 

formed?  Describe  Woulfe's  bottles.  What  atomic-  group  resembles 
potassium?  366.  What  are  the  sources  of  phosphorus  in  Nature? 
367.  What  is  the  molecular  symbol  of  ordinary  phosphorus  ?  368.  Give 
the  properties  of  this  element.  369.  How  may  red  phosphorus  be  ob- 
tained ?  370.  Name  the  compounds  of  phosphorus  and  hydrogen. 
What  takes  place  when  calcic  phosphide  is  thrown  into  water  ?  371. 
How  does  phosphoric  pentoxide  behave  when  it  is  brought  in  contact 
with  water?  372.  Describe  arsenic.  373.  To  the  formation  of  what 
gas  is  the  detection  of  arsenic,  by  Marsh's  test,  due?  How  may  the 
presence  of  antimony  be  distinguished  from  that  of  arsenic?  374. 
What  is  the  composition  of  ratsbane  ?  375,  376.  Give  the  characteris- 
tics of  antimony  and  bismuth.  What  are  the  uses  of  bismuth? 

CHAPTER   XVI.— OXYGEN. 

377.  GIVE  the  quantivalence  of  oxygen.  State  what  you  can  of  the 
modifications  of  oxygen.  378.  What  does  the  word  oxygen  mean  ? 
380.  To  what  extent  is  it  distributed  in  Nature?  381.  From  what  sub- 
stances can  oxygen  be  obtained  ?  382.  Give  properties  of  oxygen.  383. 
What  effect  has  oxygen  on  combustion  ?  385.  Under  what  conditions 
may  iron  wire  or  a  steel  spring  be  made  to  burn  with  brilliancy  ?  385. 
What  is  the  cause  of  decay  in  animal  and  vegetable  substances  ?  386. 
How  is  oxygen  related  to  the  vital  processes  ?  387.  How  is  ozone  differ- 
ent from  oxygen?  389.  What  can  be  said  of  autozone?  Give  formulas 
illustrating  the  three  forms  of  oxygen.  390.  What  is  the  common  name 
of  hydric  oxide  ?  391.  When  hydrogen  is  burned  with  oxygen,  what  is 
the  product  ?  392.  In  what  two  ways  may  the  composition  of  water  be 
demonstrated  ?  393.  Give  properties  of  water.  394.  Describe  the  forms 
which  are  the  result  of  freezing  water.  395.  What  is  said  of  the  une- 
qual expansion  of  water  ?  396.  Is  there  any  relation  existing  between 
specific  heat  of  water  and  climate?  397.  What  can  be  said  of  the 
solvent  power  of  water  ?  398.  How  may  water  be  purified  ?  400.  Give 
the  chemical  properties  of  water.  401.  State  what  you  can  of  hydric 
dioxide.  402.  What  is  known  of  the  composition  of  the  atmosphere  ? 
What  considerations  lead  us  to  the  conclusion  that  the  atmosphere  is  a 
mixture  of  gases?  403,  404.  Are  the  watery  vapor  and  carbonic  acid 
present  in  the  atmosphere  a  constant  quantity  ?  405.  What  office  does 
oxygen  perform  in  the  atmosphere  ?  What  nitrogen  ? 

CHAPTER   XVII.— SULPHUR,  SELENIUM,  TELLURIUM. 

STATE  the  quantivalence  of  sulphur.  407.  Describe  modifications  of 
sulphur.  408.  How  is  the  ordinary  form  obtained  ?  410.  Under  what 


QUESTIONS.  335 

conditions  will  ordinary  sulphur  pass  into  the  other  forms?  411.  Of 
what  use  is  plastic  sulphur  in  the  arts?  412.  Where  is  hydric  sul- 
phide found?  413.  Explain  the  method  of  liberating  hydric  sulphide? 
414.  Of  what  use  is  chloric  disulphide  in  the  arts  ?  415.  How  may 
sulphur  unite  with  oxygen  ?  416.  When  is  sulphurous  oxide  liberated? 
417.  For  what  is  S02  used?  418.  How  may  the  sulphites  be  obtained ? 
419.  Give  composition  of  sulphuric  oxide.  420.  How  early  was  sul- 
phuric acid  known  ?  How  is  it  prepared  ?  422.  What  are  the  proper- 
ties of  this  acid  ?  State  phenomena  which  occur  when  sulphuric  acid 
and  water  are  mixed  together.  What  can  you  state  of  disulphuric  acid  ? 
424.  What  do  the  words  selenium  and  tellurium  mean  ? 

CHAPTER  XVIII. — COPPER  AND  MERCURY. 

425.  FROM  what  ores  is  copper  obtained?  What  are  the  prop- 
erties of  metallic  copper  ?  What  is  verdigris  ?  What  salts  should  be 
avoided  in  the  culinary  department  ?  426.  Give  preparation  and  uses 
of  cupric  oxide.  Give  common  names  for  cupric  sulphate  and  cupric 
arsenite.  427.  State  the  properties  and  uses  of  mercury.  What  are 
amalgams  ?  428.  What  use  did  Priestley  and  Lavoisier  make  of  mer- 
curic oxide.  429.  What  is  the  antidote  for  mercuric  chloride?  430. 
Give  properties  of  calomel.  431  Under  what  name  is  mercuric  sulphide 
sold? 

CHAPTER  XIX.— CALCIUM,  STRONTIUM,  BARIUM,  LEAD. 

432.  WHERE  is  calcium  found  ?  433.  How  is  lime  obtained  ?  434. 
Describe  the  process  of  slacking.  What  is  milk  of  lime  ?  Give  prop- 
erties of  calcic  hydrate.  435.  Of  what  is  the  best  mortar  made? 
To  what  is  the  hardening  of  the  mortar  supposed  to  be  due  ?  436. 
What  is  bleaching-powder  ?  437.  Give  composition  of  gypsum.  Give 
its  uses.  438.  What  is  the  source  of  calcic  carbonate  ?  What  is  hard 
water?  439.  Through  what  mutations  does  calcic  phosphate  pass? 
440.  Give  properties  of  strontium  and  barium.  What  is  the  test  for 
sulphuric  acid  ?  What  are  the  uses  of  nitrate  of  strontium  and  baric 
sulphate  ?  441.  What  is  galena  ?  Give  the  uses  of  lead.  What  dan- 
ger may  arise  from  the  use  of  lead  pipe  ?  The  presence  of  what  salts 
in  the  water  protects  the  lead  against  its  corroding  action  ?  442.  Give 
composition  of  plumbic  monoxide  and  tetroxide.  443.  How  is  white 
lead  obtained  ?  444.  Give  properties  of  plumbic  acetate. 

CHAPTER  XX. — MAGNESIUM,  ZINC,  CADMIUM. 
445.  WHERE  does  magnesium  occur  ?     Of  what  use  is  it  in  the  arts  ? 
15 


336  QUESTIONS. 

446.  What  are  the  common  names  of  magnesic  oxide  and  sulphate  ? 

447.  How  is  zinc  obtained  ?     Give  properties.     448.  State  symbols  for 
zincic  oxide,  chloride,  and  sulphate.     Give  common  name  of  zincic  sul- 
phate.    449.  Describe  cadmium. 

CHAPTER  XXI. — IRON,  MANGANESE,  NICKEL,  AND  COBALT. 

450.  GIVE  history  and  occurrence  of  iron.  451.  Describe  the  pro- 
cess of  obtaining  wrought-iron  from  cast-iron.  452.  Give  properties 
of  iron.  What  is  the  effect  of  constant  jarring  on  wrought-iron  ?  453. 
What  is  welding  ?  What  quality  belongs  only  to  iron,  platinum,  and 
sodium?  455.  How  is  cast-iron  obtained  from  the  ore?  456.  Give  the 
origin  of  the  term  pig-iron.  457.  Properties  of  cast-iron.  458.  What 
is  steel  ?  How  produced  ?  Describe  the  Bessemer  process.  459.  What 
quality  renders  steel  valuable  in  the  arts  ?  460.  State  uses  of  ferrous 
oxide.  461.  Which  is  the  most  valuable  iron-ore  ?  462.  What  is  the 
scientific  name  of  iron  pyrites  ?  463.  Give  uses  and  composition  of 
green  vitriol.  464.  State  what  you  can  of  manganese.  465.  How  are 
nickel  and  cobalt  related  ? 

CHAPTER  XXII. — CHROMIUM,  ALUMINIUM,  AND  PLATINUM. 

466.  FOR  what  are  the  compounds  of  chromium  used  ?  467.  Give 
composition  of  dichromic  trioxide  and  chromic  trioxide.  468.  Give 
history  and  properties  of  aluminium.  Its  uses.  469.  What  compound 
gives  color  to  the  ruby  and  sapphire  ?  What  are  emery  and  corundum  ? 
470.  What  constitutes  the  basis  of  pottery?  471.  How  is  porcelain 
made  ?  What  gives  color  to  common  red  pottery- ware  ?  472.  Give 
properties  of  alum.  What  is  the  difference  between  alum  burnt  and 
unburnt  ?  473.  What  are  the  associates  of  platinum  ?  What  acid  acts 
upon  platinum  ?  What  power  has  spongy  platinum  ?  Its  uses,  in  the 
arts.  474.  How  may  platinic  tetrachloride  be  obtained  ? 

CHAPTER  XXIII.— TIN,  SILICON. 

475.  WHICH  is  harder,  gold  or  tin?  What  is  the  cause  of  the 
peculiar  crackling  sound  given  by  tin  when  bent  ?  476.  What  is  Bri- 
tannia metal?  What  elements  are  allied  to  tin?  477.  What  three 
different  modifications  has  silicon  ?  478.  Give  composition  of  silica. 
It  forms  the  bulk  of  what  minerals?  479.  What  is  the  composition 
of  the  opal?  480.  When  hydric  fluoride  acts  upon  silica,  what  gas  is 
produced?  481.  What  is  glass?  How  colored?  482.  State  how  the 
different  varieties  of  glass  are  produced. 


QUESTIONS.  337 

CHAPTER  XXIV.— CARBON. 

483.  WHAT  are  the  allotropic  forms  of  carbon?  Which  is  the 
purest  form  ?  State  what  you  can  of  the  diamond.  484.  Give  the  prop- 
erties of  graphite.  485.  How  is  charcoal  obtained  ?  486.  Its  uses.  Is 
it  an  antiseptic  ?  What  is  lamp-black  ?  487.  How  is  carbonic  monox- 
ide produced  ?  What  is  the  character  of  its  flame  ?  488.  Give  compo- 
sition of  carbonic  monoxide.  489.  How  is  carbonic  acid  prepared  ? 
490.  How  can  you  prove  that  G02  is  not  a  supporter  of  combustion,  and 
that  it  is  heavier  than  air?  What  experiment  shows  that  carbonic  diox- 
ide is  in  the  expired  breath  ?  491.  What  is  soda-water  ?  492.  Give  prop- 
erties and  uses  of  carbonic  disulphide.  493.  What  is  the  symbol  of 
cyanogen  ?  494.  Where  is  prussic  acid  found  ?  495.  Describe  potassic 
cyanide.  496.  What  is  the  popular  meaning  of  combustion  ?  How 
does  the  chemist  use  the  term  ?  497.  State  what  is  said  of  the  gradation 
of  affinities  between  oxygen  and  the  elements  of  combustible  bodies. 
498.  Show  how  explosive  combustion  takes  place.  499.  What  is  ere- 
macausis  ?  500.  What  does  intensity  of  heat  depend  upon  ?  501.  How 
does  chemical  action  produce  heat  ?  502.  What  kind  of  substances  pro- 
duce flame?  State  the  conditions  of  illumination.  503.  Describe  the 
compound  blow-pipe.  504.  What  constitutes  the  Drummond  light  ? 
505.  How  does  the  candle  burn  ?  506.  Give  a  statement  of  the  struct- 
ure of  flame.  507.  How  may  the  constant  presence  of  free  carbon  in 
the  flame  be  proved  ?  508.  Upon  what  does  the  amount  of  light  pro- 
duced depend  ?  509.  What  is  the  principle  on  which  the  safety-lamp  i.-< 
constructed  ? 

CHAPTER  XXV. — HYDROCARBONS  AND  THEIR  DERIVATIVES. 

510.  GIVE  the  composition  of  the  hydrocarbons  ?  Describe  marsh- 
gas?  Where  is  rock-oil  found?  511.  What  is  ordinary  "kerosene?" 
When  is  it  safe  to  use  a  paraffin-oil  ?  For  what  is  paraffin  used  ? 
512.  Describe  ethylene.  What  is  illuminating  gas?  513.  Why  is 
acetylene  of  special  interest?  514.  To  what  series  do  the  terpenes  be- 
long? What  are  the  oils  of  lemon  and  orange?  515.  Give  the  proper- 
ties of  benzene.  What  compound  is  a  stepping-stone  to  the  production 
of  aniline  ?  What  use  is  made  of  aniline  ?  What  other  coloring  sut- 
stances  are  mentioned  ?  516.  Give  the  general  composition  of  the 
alcohols.  From  what  is  wood-spirit  obtained  ?  517.  Give  formula  for 
common  alcohol.  Its  properties.  518.  What  is  fusel-oil  ?  519.  When 
is  wine  said  to  be  sparkling  ?  520.  Give  what  information  you  can  re- 
garding lager-beer,  ale,  and  porter.  521.  How  does  brandy  differ  from 
wine  ?  522.  Give  the  composition  of  phenol.  Mention  substances  valu- 


338  QUESTIONS. 

able  as  antiseptics.     523.  What  is  the  composition  of  the  fats  and  oils  ? 
For  what  is  glycerine  used  ?      524.    How  is  nitro-glycerine  exploded  ? 

525.  Mention  some  of  the  carbo-hydrates.      What  are  the  glucoses  ? 

526.  Give  formula  and  properties  of  cane-sugar.     528.  What  is  lactose 
used  for  ?     529.  Mention  some  substances  having  the  composition  Ci2- 
Haa  On.     What  is  varnish  ?     530.  How  does  starch  differ  from  sugar  in 
its  composition?      531.  What  are  the  properties  and  uses  of  starch? 
532.  How  may  commercial  starch  be   converted  into  dextrine?      Men- 
tion substances  isomeric  with  starch.      533.  From  what  may  cellulose 
be  obtained  ?     534.    Give  the  uses  of  cellulose.     535.  How  may  cellu- 
lose be  converted  into  pyroxylene  ?     How  does  the  explosive  force  of 
pyroxylene  compare  with  that  of  gunpowder  ?    What  is  collodion  ?     536. 
What  distinction  is  made  between  the  terms  fermentation  and  putrefac- 
tion ?    What  is  the  exciting  cause  of  fermentation  ?    537.  Give  examples 
of  ferments  and  fermentable  bodies.     What  is  said  of  yeast  ?     Mention 
different  modes  of  fermentation.     538.  What  are  the  products  of  vinous 
fermentation  ?    539.  How  is  diastase  formed  ?    540.  To  what  does  vinous 
fermentation,  if  not  checked,  pass?      What  other  name  has  vinegar? 
541.    How  are  ethers  regarded  by  the  chemist?      Describe  sulphuric 
ether.     542.  How  are  aldehydes  related  to  acids  and  alcohols  ?     What 
are  the  properties  of  acetic  aldehyde  ?     543.  From  what  is  camphor  ob- 
tained ?     544.  Give  composition  and  properties  of  chloral.     545.  What 
are  anaesthetics  ?     What  important  representative  of  this  class  have  we  ? 

CHAPTER   XXVI.— ORGANIC  CHEMISTRY.     (Continued.) 

546.  FROM  what  is  formic  acid  obtained  ?  547.  What  is  the  com- 
position of  acetic  acid  ?  548.  Give  method  of  preparing  butyric  acid, 
and  its  properties.  Where  is  glycocholic  acid  found  ?  549.  What  can 
be  said  of  lactic  acid  and  succinic  acid  ?  Where  is  malic  acid  found  ? 
What  are  the  uses  of  tartaric  acid  ?  550.  Give  composition  of  benzoic 
acid.  551.  Give  history  of  salicylic  acid.  552.  What  is  the  acid  ob- 
tained from  the  fruits  of  the  orange  family  called?  For  what  purposes 
is  gallic  acid  used?  553.  What  is  the  distinguishing  characteristic  of 
tannic  acids  ?  What  is  the  basis  of  writing-ink  ?  554.  Give  the  anti- 
dote for  oxalic  acid.  Its  uses.  555.  What  can  be  said  of  Rochelle 
salts  and  cream-of-tartar  ?  556.  Have  the  organic  alkaloids  been  arti- 
ficially produced  ?  What  substance  precipitates  the  organic  bases  ? 
557.  Give  the  name  of  the  alkaloid  contained  in  tobacco.  558.  What 
narcotic  is  the  active  principle  of  opium  ?  559.  From  what  is  strych- 
nine obtained  ?  How  does  this  alkaloid  affect  the  nervous  system  ? 
560.  What  organic  bases  are  obtained  from  Peruvian  bark?  561.  To 
what  are  the  stimulating  effects  of  tea  and  coffee  due  ?  562.  Describe 


QUESTIONS.  339 

the  albuminoids.  563.  Where  is  albumen  found  ?  In  what  two  modifi- 
cations does  it  exist  ?  564.  What  is  said  of  musculine,  fibrine,  and  glu- 
ten ?  565.  Give  the  essential  constituent  of  milk.  What  is  said  of  the 
constitution  of  cow's  milk  ?  566.  What  use  is  made  of  gelatine  ?  From 
what  is  chitine  obtained  ?  567.  What  was  the  first  organic  compound 
artificially  produced  ?  568.  Give  the  name  of  the  compound  occurring 
in  the  juice  of  flesh.  569.  Has  pepsine  ever  been  perfectly  isolated? 

570.  What  constitutes  the  chief  part  of  the  red  globules  of  the  blood  ? 

571.  What  are  some  of  the  products  of  putrefactive  changes?     How 
may  putrefaction  be  prevented  ?     572.  What  is  said  of  ferment  diseases  ? 


PRONUNCIATION  OF  SOME  TECHNICAL  WORDS 
AND  PROPER  NAMES  USED  IN  THIS  WORK. 


TECHNICAL     WORDS. 


A9'-e-tate. 

A-cet'-ic. 

A-ce'-tous. 

A-cet'-y-lene. 

Al-bu'-men. 

Al'-de-hyde. 

Al-iz'-avine. 

Al-kal'-am-ide. 

Al-lo-trop'-ic. 

Al-lot'-ro-pism. 

Al-u'-min-a. 

Al-u'-min-ic. 

Al-u-min'-i-um. 

Am'-ad-in. 

Am'-ide. 

Am'-ine. 

Am-mo'-nic. 

Am-yl'-ic. 

An-ses-thet'-ics. 

An'-il-ine. 

Ant'-o-zone. 

Ar'-ab-in. 

Ar-gen'-tic. 

Ar'-sen-ic  (noun). 

Ar-sen'-ic  (adj.). 

A-ther'-mic. 

A-tom'-ic. 

At-om-i9'-it-y. 

Ben-zo'-ic. 

Bo-ra9'-ic. 

Bro'-mine. 

Bu-tyr'-ic. 

Caf-fe'-me. 

Cam'-er-a  ob-scu'-ra. 

Caoutchouc  (Koo'-chook) 

Cap'-il-la-ry. 

Cap'-si-cme. 


Chi  tine  (ki'-teen). 
Chlorine  (Klo'-rin). 
Co'-balt. 
Col-li-ma'-tor. 
Col-loid'. 
Cry-oph'-o-rus. 
Di-al'-y-sis. 
Di'-as-tase. 
Di-a-ther'-man-cy. 
Dif-fu'-sate. 
Dy-ad'-ic. 
E-lec-trol'-y-sis. 
Er-e-ma-cau -sis. 
Eth'-yl. 
Eth'-yl-ene. 
Flu'-o-rme. 
Gly9'-e-rine. 
Gly-co-chol'-ic  (/col). 
Gly '-co-gen. 
Go-ni-om'-e-ter. 
Has-mo-glo'-bme. 
Hep'-tad. 
Hip-pu'-ric. 
Ho-mo3-o-mor'-phous. 
Hy-dray'-id. 
Hy-drox'-yl. 
I'-o-dine. 
I-som'-er-ides. 
I-som'-er-ism. 
I-so-mor'-phism. 
j    Laev'-u-lose. 
Lith'-arge. 
Lith'-i-um. 
Mer-cu'-ric 
Mer'-cu-rous. 
Met-ath'-e-sis. 
Meth'-yL 


PRONUNCIATION,   ETC. 


341 


Mol'-e-cule. 

Mon-ad'-ic. 

Mor'-phine. 

Mo-lyb-de'-num. 

Nic'-o-tine. 

Ni-trog'-e-uous. 

Ni'-tryl. 

O-le-fi'-ant. 

Par'-af-fin. 

Per-is'-sad. 

Phe'-nyl. 

Phos-phor'-ic. 

Pho'-to-sphere. 

Pip'-er-me. 

Plat  in'-ic. 

Plat'-i-num. 

Py-ri'-tes. 

Pyr-o-gal'-lic. 

Quan-tiv'-a-lence. 

Quinine  (Kwe-mne1,  or  Kurin'-in). 

Saccharine  (Sak1 -a-rin). 

Sa-li-cyl'-ic. 


Sa-li'-va. 

Sel'-e-nite. 

Se-le'-ni-um. 

Sil-i9'-ic. 

Sil'-ic-on. 

Spec'-tro-scope. 

Spiegeleisen  (Spe' -ghel-i-sen). 

Sta-lac'-tite. 

Sta-lag-mite. 

Ste'-ar-me. 

Strychnine  (Strik -nin}. 

Suc-9in'-ic. 

Sul-phu'-ric. 

Sul'-phur-ous. 

Tar-tar'-ic. 

Tet'-rad. 

The'-ine. 

Ther-mot'-ic. 

Tho-ri'-num. 

Tourmaline  (Toor'-ma-lin}. 

U-niv'-a-lent. 

U'-re-a. 


PEOPEK     NAMES. 


Al-deb'-a-ran. 

Ampere  (Ang-pdre1). 

A-vo-gad'-ro. 

Berthelot  (Ber1 -tel-o). 

Bes'-sem-er 

Bournon  (Boor-nong). 

Bunsen  (Boon -sen). 

Chaptal  (Shap'-tal). 

Clausius  ( Clow -si -us). 

Daguerre  (Day-yair). 

De  la  Rive  (Reeve\ 

Descartes  (Day-cart'}. 

Du    Bois-Reymond    (X>u-bwd-Ray' 

mong}. 

Dumas  (Du-mah'}. 
Durkheim  (Door'-kime). 
Dutrochet  (Du-tro'-shay). 
Ehrenberg  (A '-ren-berg}. 
Fraunhofer  (Frown' -ho- fer). 
Galvani  ( Gal-vah' -nee}. 
Gay-Lussac  ( Gati-ee-lti&'-sac}. 
Gerharat  ( Gair'-hart). 


Haidlen  (Hlde-Un). 
Hauy  (Ah'-ii-y}. 
Joule  (Jole). 


Klaprcth  (K  lap'  -rote}. 
Leverrier  (Le-ver  -re^a). 
Leyden  (Li'  -den). 
Liebig  (Lee  -big}. 
Marignac  (Mar-in1  -yac}. 
Matteucci  (Mat-tu'-tshee). 
Mayer  (My'-er). 
Montgolfier  (Afona-gol  '-fec-ct}. 
Oersted  (  Ur'-sted}. 
Par-a-cel'-sus. 
Reaumur  (Ray  -o-mur). 
Regnault  (Rain'-yole}. 
Ruhmkorff  (Room'-korf) 
Scheele  (Shay1  Jay). 
Schellen  (Shel'-len}. 
Schonbein  (Shane1  -bine). 
Vogel  (Fo'-ghet). 
Wohler  (  Vatt-er). 


INDEX. 


Absorption  of  heat,  52,  53;   of  spectral 

lines,  110-114. 
Acetate  of  lead,  250. 
Acetic  acid,  308. 

aldehyde.  306. 
Acetylene.  291. 

Acids,  constitutions  of,  151 ;  kinds  of,  153. 
Acid,  arsenious,  211. 

acetic,  305,  30S. 

benzole,  310. 

boric,  197. 

butyric,  309. 
Acid,  carbolic,  295. 

carbonic,  275. 

carminic,  292. 

citric,  311 

di  sulphuric,  239. 

formic,  303. 

gallic,  311. 

gallotannic,  311,  313. 

glycocholic,  309. 

hippuric,  310. 

hypochlorous,  179. 

lactic,  309. 

malic,  309. 

meta -phosphoric,  210. 

muriatic,  178. 

nitric,  202. 

nitrous,  201. 

Nordhausen,  239. 

ortho-arsenic,  212. 

ortho-phosphoric,  210. 

oxalic,  312. 

prussic,  278. 

pyroligneous,  309. 

pyrophosphoric,  210. 

silicylic,  310. 

silicic,  268. 

succinic,  304,  309. 

su  phuric,  237. 

sulphurous,  236. 

tannic,  311. 
Acid-former,  139. 
Acroleine,  296. 
Actinism,  88. 
Actinometry,  91. 

Adhesion,  25;  of  liquids  to  solids.  25;  of 
gases  to  liquids,  28;  of  gases  to  solids,  28. 
Alabaster,  246. 


Albumen,  315 ;  vegetable,  316. 
Albuminous  substances,  315. 
Alcohols,  292-296. 
Alcohol,  common,  293. 
Alcohol,  methyl,  293. 

ethyl,  293. 

amyl,  294. 

Aldehydes,  305,  306. 
Ale,  -294. 
Alizarine,  292. 

Alkalamides,  naming  of,  167. 
Alkaloids,  organic,  313. 
Allotropism,  153. 
Alum,  264. 
Alumina,  263. 
Aluminic  oxide,  263. 

silicates,  '2(!3. 
Aluminium,  26J. 
Amadin,  300. 
Amethyst,  268. 
Amides,  naming  of,  167. 
Ammonia,  199. 
Ammonic  chloride,  204 

hydrate,  204. 

nitrate,  206. 

sulphate,  206. 

carbonates,  206. 
Ammonium,  206. 
Anaesthetics,  308. 

Analysis ;  proximate ,  ultimate :  qualita- 
tive ;  quantitative,  1.8 ;  of  molecule,  137. 
Aniline.  292. 
Animal  electricity.  79. 
Anomalous  bodies,  153. 
Anthracene,  292. 
Antimony,  212. 
Antozone,  221. 
Aqua  ammonia,  204. 
Aqua  regia.  197,  203. 
Argentic  chloride,  195. 

mom  xide,  195. 

nitrate,  196. 
Arrack,  294. 
Arsenic.  210-212. 

trioxide,  211 

disulphide,  212. 

trisulphide,  212. 
Arseniuretted  hydrogen,  210. 
Artiads,  145,  214. 
Astatic  needle,  77. 
Atmosphere,  228. 


INDEX. 


343 


Atom,  24,  134.  135;  in  chemistry,  136; 

symbols  of,  187. 
Atomic  heat,  162. 

theory,  134 ;  revival  of,  185. 
Atomicity,  141.  14'2,  145. 
Attractions,  15;  molecular,  24 ;  capillary, 

26;  chemical,  12t>. 
Auric  chloride,  197. 

cyanide,  197. 
Avogadro'a  law,  158 ;  chemical  application 

oi?180. 


Balance,  16. 
Balsams,  298. 
Baric  oxide,  247. 

chloride  dihydrate,  248. 

sulphate,  248. 
Barium,  247. 

Bases,  constitution  of.  151 ;  kinds  of,  153. 
Bassorin,  298. 

Battery,  galvanic,  72 ;  DanielPs,  78. 
Benzine  series,  291. 
Benzoic  acid,  310. 
Benzol,  291. 
Bessemer  process,  258. 
Binary  theory,  139. 
Bismuth.  213. 
Bleaching-powder,  245. 
Blow-pipe.  232. 
Blue  vitriol  242. 

Bodies,  compound  and  simple,  13. 
Boiling-point  55. 
Bonds,  143. 144. 
Boric  acid,  197. 
Borax,  198. 
Boron,  197. 
Brandv,  294. 
Brass,  241. 
Britannia  metal,  267. 
Bromine,  181. 
Bronze.  241. 
Brucine.  314. 
Burning-fluid.  291. 
Butyric  acid,  309. 
Butter,  318. 

C. 

Cadmium.  252. 
Caesium,  193. 
Caffeine,  315. 
Calcic  oxide,  244. 

hydrate,  244. 

sulphate,  246. 

"       dihydrate,  246. 

carbonate,  246. 

phosphate,  247. 

pxalate;  312. 
Calcium  group,  244. 
Calomel,  243. 
Caloric,  62. 
Camera-obscura,  94. 
Camphene.  291. 
Camphor.  807. 
Candle,  how  it  burns,  283. 
Caoutchouc,  299. 
Capillarity,  reversed,  27. 


Capillary  attraction,  26,  27. 

Capsicine,  314. 

Carbolic  acid,  295. 

Carbon,  270-287 ;  history  and  properties 

of,  270;  allotropic  forms  of,  270. 
Carbonate  of  lead,  249. 
Carbonic  acid,  275. 
Carbonic  monoxide,  274. 
dioxide,  275. 
disulphide,  278. 
Caseine,  317. 
Cast-iron,  256. 
Catalysis,  131. 
Caustic  potash,  189. 
Caustic  soda,  187. 
Cellulose,  301. 
Cement,  245. 
Cementation,  258. 
Change  by  pairs.  146. 
Charcoal,  272. 

uses  of,  278. 

Chemical  action,  character  of,  127;  con- 
ditions of,  129;  intensities  of,  131. 
attraction,  gradations  in,  129. 
equations,  16s. 
force,  127;    characteristic  effect*  of, 

128;  range  of,  131. 
formula,  168. 
physics,  13. 

rays.  83 ;  variations  of,  91,  92. 
reactions  of  light,  £3. 
types,  140. 
Chemism,  127, 128. 
Chemistry,  basis  of;  132;  theoretical,  134 

of  carbon  compounds,  157. 
Chitine,  318. 
Chloral,  807. 

hydrate,  307. 
Chloric  disulphide,  235. 
monoxide,  180. 
tetroxide,  180. 
acid,  180. 
trioxide.  179. 

Chlorine,  175;  preparation  of,  176;  prop- 
erties of,  176 ;  uses  of,  177 ;  combustion 
of  turpentine  in,  178. 
Chloroform,  807. 
Chondrine,  318. 
Chromic  oxide.  262. 

trioxide,  262. 
Chromium,  261. 
Cinchonine,  315. 
Cinnabar,  243. 
Citric  acid,  311. 
Cleavage.  43. 
Coal-oil.  238. 
Coal-tar.  290. 
Cobalt,  260. 

Cobaltous  chloride,  261. 
Cohesion,  25,  26 ;  influence  of,  130. 
Coke,  290. 
Collimator,  103. 
Colloids.  31. 

Colored  lights,  varying  effects  of,  96. 
Collodion,  802. 
Colors,  cause  of  81 . 

Combining  capacity.  141 ;  volumes,  162. 
Combination,  control  of.  144. 
Combining  volumes,  theory  of,  158, 162. 


344 


INDEX. 


Combustion,  64,  279;  rapid,  280;  slow, 
•281 ;  heat  of,  281 ;  spontaneous,  281. 

Common  salt,  185. 

Compounds,  128;  metameric,  157;  poly- 
meric, lob. 

Compound  blow-pipe.  282. 

Condensation  of  gases,  60. 

Conductors,  65. 

Copper,  241. 

Corrosive  sublimate,  243. 

Cream-of-tartar,  312. 

Creosote,  295. 

Crith,  161. 

Cryophorus,  58. 

Crystallization,  35-46 ;  phenomena  attend- 
ing, 38. 

Crystalloids,  81. 

Crystals,  natural,  86;  artificial,  36;  by 
solution,  86 ;  by  fusion,  37 ;  by  sub- 
limation, 37  ;  in  the  solid  state,  87 ;  by 
decomposition,  38 ;  forms  of,  40 ;  axes 
of,  40 ;  elements  of  crystalline  form,  40 ; 
systems  of,  41,  42. 

Cupric  oxide,  241. 
sulphate,  242. 
arsenite,  242. 

Cyanogen,  278. 


D. 

Daguerreotype,  95. 

Decomposition,  128. 

Definite  proportions,  law  of,  132. 

Density,  22. 

Derivation  of  form,  43. 

Developing  a  photograph,  95. 

Dew,  52 

Dew-point,  58. 

Dextrine,  300. 

"Dextrose,  297. 

Diamagnetism,  70. 

Diamond,  271. 

Diastase,  304. 

Diathermancy,  53. 

Dichromic  trioxide,  262. 

Diffusion,  of  gases,  29;  rate  of,  29;  of 
liquids  and  solids  through  gases,  30 ;  of 
liquids,  31;  rate  of,  31;  of  gases  thronrrh 
liquids.  32 ;  of  solids  through  liquids, 
33 ;  of  gases  through  solids,  35. 

Dimorphism,  45. 

Dispersion,  101:  power  of  crown-glass. 
101;  of  flint-glass,  101;  of  bisulphide  of 
carbon,  101. 

Distillation,  60. 

Distilled  liquors,  294. 

Double  solar  spectrum,  124. 

Draper's  researches,  108. 

Prummond  light,  283. 

Dualism,  139. 


E. 

Ebullition,  55. 

Electricity,  65-80 :  animal,  79 ;  magnetic. 

73 ;  thermo,  77 ;  voltaic,  71 ;  influence  of, 

130. 
Electric  light,  spectrum  of,  99. 


Electric  lamp,  100. 

tension,  66. 
Electrodes,  72. 
Electrolysis,  75. 
Electro-magnetism,  76. 
Electrotype,  76. 
Elements,  128,  129;  organic,  156;  in  a 

free  state,  147;  naming  of,  164;  peris - 

sad,  169 ;  artiad,  214. 
Elements  in  sun,  121 ;  in  stars,  122. 
Epsom  salts,  251,  312. 
Eremacausis,  218. 
Ethers,  805. 
Ethyl,  149. 
Ethylene,  290. 
Ethylic  ether,  305. 
Expansion  of  solids,  46 ;  of  liquids,  47 ;  of 

gases,  47. 

F. 

Fats  and  oils,  295. 
Fermentation,  302-305. 

vinous.  304. 

saccharous,  304. 

acetous.  805. 

lactic,  309. 
Ferments,  303. 
Fermentable  bodies,  303. 
Ferment  diseases,  320. 
Ferric  carbides,  256. 

disulphide,  259. 
Ferrous  oxide,  259. 

sulphate,  260. 

carbonate,  260. 
Fibrine,  816. 
Fire-damp,  288. 
Flame,  282;   structure  of,  284;  effect  of 

temperature  on,  285. 
Fluorescence,  88. 
Fluorine,  180. 
Force,  indestructible,  12. 
Forces,  radiant,  motions  of,  80. 
Formic  acid,  808. 
Fraunhofer's  lines,  107,  111,  115. 
Freezing  mixtures,  55. 
Fusel-oil,  294. 

G. 

Gallotannic  acid,  312. 
Galvanic  battery,  72. 
Galvanism.  71  ;  quantitv  and  intensity 

of,  74. 

Gas,  illuminating,  290. 
Gases,  20,  21 ;  condensation  of,  60. 
German  silver,  241. 
Gelatine,  318. 
Gin.  295. 

Glass,  269 ;  varieties  of,  269. 
Glauber's  salt,  187. 
Gluten,  316. 
Glycerine,  296,  304. 
Glycocholic  acid,  309. 
Glycogen,  800. 

Gold,  196 ;  properties  of,  197. 
Graphite.  271. 
Gravity,  15. 
Green 'vitriol,  260. 


INDEX. 


345 


Gum,  298. 
Gum-arabic,  298. 
Gun-cotton,  302. 
Gunpowder,  191. 
Gypsum,  246. 


,    Isomerid.es,  158. 
Isomerism,  155,  157. 
Isomorphism,  44. 


II. 


ip,  183. 
Haloids,  154. 
Haemato-crystalline,  319. 
Haemoglobine.  319. 

Heat,  46-65 ;    its  effects.  46 ;  expansion 
by,  47;  measurement  of,  47;  transfer- 
ence, 49 ;  conductions  of,  49 ;  convec- 
tion of,  51 ;  radiation  of,  51 ;  kinds  of 
radiant.  52;  absorption  of,  by  aqueous 
vapor,  53;  latent,  54;  specific,  54;  na- 
ture of,  61 ;  relation  to  chemical  action,  ; 
61 ;  as  a  mode  of  motion,  63. 
Heavy  spar,  248. 
Horn  silver,  195. 
Hydracids,  154. 

Hydrates.  152, 153 ;  quantivalence  of,  153. 
Hydric  chloride,  17S. 
chlorate,  179, 180. 
perchlorate,  179. 
fluoride,  181. 
bromide,  183. 
iodide,  183. 
nitride,  199. 
nitrate,  202. 
phosphide,  208. 
arsenide,  210. 
oxide.  221. 
dioxide,  228. 
sulphide,  283. 
sulphite,  236. 
sulphate,  237. 
cyanide,  278. 
Hydrides,  172. 

Hydrocarbons  and  their  derivatives,  287- 
292. 


Hydrogen,  169-175;  occurrence  in  Nature,  j 
170;  preparation  of,  170;  chemical  prop- 
erties   of,    172;    condensation  of,  174; 
occlusion  of,  174. 

Hvdrogenium.  174. 

Hydrometer,  21. 

Hydro-sodic  borate,  198. 

Hygrometer,  59. 


Illuminating  gas.  290. 

India-rubber,  299. 

Induction,  electrical  66;    magnetic,    69; 

chemical,  130;   theory  of,  67;  induced 

currents,  74. 
Inflammable  air,  169. 
Insulators,  65. 
Interference  of  light,  82. 
Inuline,  300. 
Invisible  image,  94. 
Iodine,  182. 
Iridium,  266. 
Iron,  253;  history  and  occurrence  of,  253; 

properties,  254;    preparation    of,    253; 

uses  of,  256. 


Kerosene. 


Lactic  acid,  309. 

Lactose,  298. 

Laevulose,  297. 

Lager-beer,  294. 

Lamp-black,  274. 

Latent  heat,  54. 

Laughing  gas.  201. 

Law  defined.  11. 

Law  of  Avogadro,  158;  of  definite  propor- 
tions, 132 ;  multiple  proportions,  133. 

Lead,  248. 

Legumine,  317. 

Light,  80-127;  analysis  of,  80 ;  wave-theory 
of,  81 ;  interference  of,  82 ;  polarization 
of,  83;  double  refraction  of,  87 ;  chemis- 
try of,  88;  refrangibility  of,  89 ;  effect,  on 
vegetation,  of  rays  of,  "92 ;  chemical  re- 
actions, 93;  ifcomposition  of,  98;  ab- 
sorption of,  110. 

Ugnine,  301. 

Lime,  244. 

Limestone.  246. 

Lines,  absorption,  112;  reversal  of,  113; 
what  indicated  by,  109. 

Liquefaction,  54. 

Liquids,  20. 

Litharge,  249. 

Lithium,  193. 

Litre,  15. 

Luminous  spectrum,  98. 

Lunar  caustic,  196. 

M. 

Magnesia.  251. 
Magnesic  oxide.  251. 

sulphate,  251. 
Magnesium  group,  250. 
Magnetic  induction,  69. 

oxide.  259. 
Magnetism,  63-71 ;  kinds  of  magnets,  68 ; 

induction  of,  69. 
Malic  acid,  309. 
Malt,  305. 
Manganese.  260. 
Manganic  dioxide,  260. 
Marsh-pas,  287,  288. 
Marsh's  test,  211. 
Matter  denned,  12. 

indestructible,  12. 

interior  structure,  23 ;  porosity  of  23 ; 
motions  of  internal  parts  of,  23 ;  divisi- 
bility of,  24. 

measurement,  14. 
Matter  and  force,  12. 
Melting-point,  54. 
Mercuric  oxide,  243. 

chloride,  243. 

sulphide,  243. 


346 


INDEX. 


Mercurous  chloride,  243. 

Mercury,  241. 

Metathesis,  13T. 

M  eta-acids,  153. 

Methane,  288. 

Methyl,  149. 

Metrical  measures,  15. 

Metre,  15. 

Miasms,  320. 

Milk,  317. 

Milk-sugar,  298. 

Molecular  motions,  45. 
weight,  unit  of,  160. 

Molecule,  24,  134,  135 ;  in  physics,  135 ;  in 
chemistry,  135 ;  structure  of,  147 ;  space 
relations  of,  158 ;  size  of,  159. 

Morphine,  313 

Mortar  and  cement,  245. 

Mucilage,  298. 

Multiple  proportions,  law  of,  133. 

Muriatic  acid,  178. 

Musculine,  316. 

N. 

Naming  elements,  164;   compound  radi- 
cals, 164;  binary  compounds,  165;  salts, 
acids,  and  bases,  167 ;  amides,  amines, 
and  alkalamides,  167. 
Naphthaline,  292. 
Nascent  state,  181. 
Nature,  order  of,  11. 
Negatives  and  positives,  72,  95. 
Nickel,  260. 
Nicotine,  313. 
Nitre,  190. 
Nitric  acid,  202. 

monoxide,  201. 

dioxide,  201. 

trioxide,  201. 

tetroxide,  201. 

pentoxide,  201. 

Nitrogen,  198;  preparation  and  proper- 
ties of,  199. 

Nitrogen  group,  198-213. 
Nitro-benzine,  292. 

glycerine,  296. 
Nitryl,  151,  302. 
Nomenclature,  163-169. 
Normal  salts,  153. 

O. 

Occlusion,  35, 174. 

Olefiant  gas,  290. 

Olefine  series,  289. 

Olein,  295. 

Opal,  268. 

Opium,  314. 

Organic  alkaloids,  313. 

Organic  elements,  156. 

Orthoacids,  153. 

Osmium,  266. 

Osmose,  of  gases,  29;  of  liquids,  82. 

Oxalic  acid,  313. 

Oxygen,  214-231 ;  modifications  of,  214 ; 

occurrence  of,  215;  preparation  of,  215; 

properties  of.  216;  combustion  in,  217; 

relation  to  life  of,  218. 
Ozone,  219 ;  properties  of,  220. 


P. 

Palladium,  266. 
Palmitine,  296. 
Paraffins,  287,  289. 
Paris  green,  242. 
Pearlash,  190. 
Pectin,  298. 

Ferissads,  145 ;  inconvertible,  146. 
Petrifaction,  268. 
Petroleum,  288. 
Phenol,  295. 

Phenomenon  defined,  11. 
Phlogiston,  138. 
Phosphorescence,  87. 
Phosphoric  pentoxide,  210. 
Phosphorus,   206;    distribution  of,    206; 
properties  of,  207 ;  modifications  of,  207. 
208. 

Phosphuretted  hydrogen,  208. 
Photography,  98;  celestial,  96. 
Physical  verifications,  161. 
Physical  properties  of  matter,  12. 
Pig-iron,  257. 
Pile,  voltaic,  72. 
Piperine,  314. 
Platinic  tetrachloride,  265. 
Platinum-black,  265. 
Platinum  group,  265. 
Plumbago,  '271. 
Plumbic  monoxide,  249. 

carbonate,  249. 

tetroxide,  249. 

acetate,  250. 
Pneumatic  trough,  171. 
Polarity,  146. 
Polarization,  85. 
Porcelain.  263. 
Porter.  294. 
Potassic  monoxide,  189. 

hydrate,  189. 

chloride,  189. 

carbonates,  190. 

nitrate,  190. 

sulphate,  192. 

silicate,  192. 

cyanide,  279. 

Potassio-aluminic  sulphate,  264. 
Potassium,  188. 
Prefixes.  166. 
Press-cake.  191. 

Prevision  the  best  test  of  science,  12. 
Primary  rays.  99. 
Prisms,  8');  combination  of,  101;   trains 

of,  102. 
Proportions,  definite,  132;  multiple,  133; 

equivalent,  184. 
Prussic  acid,  278. 
Puddling,  254. 
Putrefaction,  802. 
Pyroxylene,  301. 

Q. 

Quantivalence,  141,  142;  its  expressions, 

142 ;  varying,  144. 
Quinine,  314. 
Quartation,  197. 
Quartz,  268. 


INDEX. 


347 


Radiant  motion,  transmission  of,  82. 
Radicals,    theory  of,    148;    simple,  148; 
compound,  149 ;  quantivalencs  of,  149. 
Rays,  chemical.  S3. 
Refraction,  double,  87. 
Refrangibility  of  invisible  rays,  89. 
Resins,  298. 
Rhodium,  266. 
Rochelle  salts,  312. 
Rubidium,  193. 
Rum,  294. 
Ruthenium,  266. 


Saccharine  bodies,  296-502. 
Safety-lamp,  2S6. 
Sal-ammoniac,  204. 
Sahcine,  310. 
Salicylic  acid,  310. 
Saltpetre,  190. 

Salts,  constitution  of,  152 ;  classes  of,  153. 
Saturation,  34. 
Science  defined,  11. 
Selenium,  240. 

Separation  of  solids  from  solution,  34. 
Silica,  267. 
Silicic  acid,  268. 
dioxide,  267. 
fluoride,  268. 
Silicon,  267. 
Silver,  194 ;  properties  and  uses,  195.    (See 

ARGENTIC.) 
Snow-crystals,  224. 
Soap.  18^,  192, 193. 
Sodic  chloride,  184. 

carbonates,  136, 187. 
hydrate,  1S7. 
sulphate,  187. 
nitrate,  187. 
silicates,  192. 
Sodium  group,  184., 
Solar  envelope,  ItSr* 

prominences,  120. 
Soluble  glass,  192. 
Solution.  33. 
Specific  gravity,  of  liquids,  20 ;  of  gases, 

20. 
Specific  heat,  54. 

volume,  17 ;  weight,  17. 
Spectral   lines,  106;  indications  of,  109; 

coincidence  of  bright  and  dark.  110. 
Spectroscope,  103:  essential  parts  of,  103: 

direct  vision,  104 ;  mounted,  104. 
Spectroscope  in  steel-making.  116. 
Spectrum,  solar,  99;  luminous,  98;  of  the 

electric  light  99;  measuring  the,  103: 

Newton's,  106 ;  affected  by  pressure  or 

density.  109 ;  lines.  110 ;  double,  124. 
Spectrum  analysis.  99-127. 
Speculum  metal,  241. 
Spheroidal  state.  56. 
Spieseleisen,  257. 
Stannic  dioxide,  266. 
Star,  conflagration  of  a,  122. 
Starch,  299. 
Stars,  motions  of,  125, 


Stearine.  295. 

Steel,  258. 

Stibic  trioxide,  213. 

trisulphide,  213. 
Stone-ware.  264. 
Strontium,  247. 
Strychnine,  814. 
Substitution  theory,  140. 
Succinic  acid.  309. 
Sugar,  grape,  297. 

fruit.  297. 

cane.  297. 

milk.  298. 

Sulphur  group.  231-241. 
Sulphuretted  hydrogen,  233. 
Sulphuric  oxide",  236. 

acid.  237 ;  manufacture  oi,  237,  238. 

properties  and  uses,  239. 
Sulphurous  oxide,  235. 

acid.  236. 

Sun,  elements  in,  121. 
Symbols  of  atoms,  137. 
Synthesis.  137. 
Systems  of  crystallization,  41. 

T. 

Tannic  acid,  311. 

Tannin.  311. 

Tartaric  acid.  309. 

Tele-spectroscope,  117. 

Tellurium.  240. 

Terpenes,  291. 

Tetraferrio  carbide,  258. 

Theine.  315. 

Theobromine,  315. 

Theory  of  acids,  bases,  and  salts.  151: 
of  radicals,  148;  of  polarization,  86:  ot 
absorption,  114;  atomic,  134;  progress 
of  chemical  138;  binary,  139;  unitary. 
139;  substitution.  139";  of  chemical 
types,  140 ;  of  isomerism  and  allotro- 
pism.  155;  of  combining  volumes,  158; 
of  effects,  162. 

Thermo-electricity,  77. 

Thermometer,  47":  mercurial,  47;  scales, 
48. 

Thorium,  267. 

Tin.  266. 

Titanium.  267. 

Touch-paper.  191. 

Triferrc  tetroxide.  259. 

Turpentine  series.  291. 

Type-,  chemical,  140. 

U. 

Unitary  theory.  139. 


Vapor,  volume  and  density  of,  59 ;  elastic 
force  of,  59. 

Vaporization,  57;  heat  of,  57  ;  cooling  ef- 
fects of.  58. 

Varnishes,  299. 

Vegetation,  influence  of  light  on,  92. 

Verdigris,  241. 

Vermilion,  244. 


348 


INDEX. 


Vinegar,  309. 
Volatile  liniment,  201. 
Volumes,  combining,  162. 
Voltaic  electricity,  71-76. 

W. 

Water,  221 ;  production  of,  222 ;  compo- 
sition of,  222;  properties  of,  22£>;  un- 
equal expansion  of,  225;  specific  heat 
of,  225;  solvent  power  of,  226;  purifica- 
tion of,  227;  chemical  properties  of,  227 

Water-former,  139. 

Weights,  16 ;  metrical  standard,  17. 

Welding,  255. 

Whiskey,  294. 

White  lead,  249. 


White  vitriol,  252. 
Wine,  294. 
Wood-spirit,  293. 


Yeast,  304. 


Zinc,  251. 

Zincic  sulphide,  251. 

carbonate,  2c,l. 

oxide,  252. 

silicate,  251. 

chloride,  252. 

sulphate,  252. 
Zirconium,  267. 


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recast,  enlarged,  and  rewritten.  By  HENRY  MAUDSLET,  M.  D.,  author 
of  "  Physiology  of  the  Mind,"  "  Responsibility  in  Mental  Disease," 
etc.  One  vol.,  12mo,  580  pages.  Price,  $2.00. 

SUMMARY  OF  CONTENTS:  Sleep  anrl  Dreaming;  Hypnotism,  Somnambulism,  and 
Allied  States;  The  Causation  and  Prevention  of  Insanity:  (A)  Etiological;  The  Cau- 
sation and  Prevention  of  Insanity:  (B)  Pathological;  The  Insanity  of  Early  Life;  The 
Symptomatology  of  Insanity ;  Clinical  Groups  of  Mental  Disease;  The  Morbid  Anat- 
omy of  Mental  Derangement ;  The  Treatment  of  Mental  Disorders. 

THE  CHEMISTRY  OF  COMMON  LIFE.    By  the 

late  JAMES  F.  W.  JOHNSTON,  F.  R.  S.,  etc.,  Professor  of  Chemistry  hi 
the  University  of  Durham ;  author  of  "  Lectures  on  Agricultural 
Chemistry  and  Geology  " ;  "  Catechism  of  Agricultural  Chemistry 
and  Geology,"  etc.  A  new  edition,  revised,  enlarged,  and  brought 
down  to  the  Present  Time,  by  ARTHUR  HERBERT  CHURCH,  M.  A., 
Oxon..  author  of  "Food:  its  Sources,  Constituents,  and  Uses"; 
"  The  Laboratory  Guide  for  Agricultural  Students  "  ;  "  Plain  Words 
about  Water,"  etc.  Illustrated  with  Maps  and  numerous  Engravings 
on  Wood.  In  one  vol.,  12mo,  592  pages.  Price,  $2.00. 

SUMMARY  OF  CONTENTS  :  The  Air  we  Breathe;  The  Water  we  Drink ;  The  Soil  we 
Cultivate:  The  Plant  we  Rear ;  The  Bread  we  Eat;  The  Beef  we  Cook ;  The  Beverages 
we  Infuse;  The  Sweets  we  Extract;  The  Liquors  we  Ferment;  The  Narcotics  we  In- 
dulge in;  The  Poisons  we  Select;  The  Odor?  we  Enjoy;  The  Smells  we  Dislike;  The 
Colors  we  Admire;  What  we  Breathe  and  Breathe  for;  What,  How,  and  Why  we 
Digest;  The  Body  we  Cherish;  The  Circulation  of  Matter. 

in. 

PROGRESS  AND  POVERTY.  An  Inquiry  into  the 
Cause  of  Industrial  Depressions  and  of  Increase  of  Want  with  In- 
crease of  Wealth:  The  Remedy.  By  HENRY  GEORGE.  One  vol., 
12mo.  512  pages.  Cloth.  Price,  $2.00. 

I  propose  to  seek  the  law  which  associates  poverty  with  progress,  and  increases 

in  th 


want  with  advancing  wealth;  and  I  believe  that  in  the  explanation  of  this  paradox  we 
shall  find  the  explanation  of  those  recurring  seasons  of  industrial  and  commercial  pa- 
ralysis which,  viewed  independently  of  their  relations  to  more  general  phenomena, 
seem  so  inexplicable."—  Extract  from  Introduction. 

GREAT    LIGHTS     IN    SCULPTURE     AND 

PAINTING.     A  Manual  for  Young  Students,     By  S.  D.  DOREMUS. 

One  vol.,  1 2mo.     Cloth.     Price,  $1.00. 

"  This  little  volume  has  grown  out  of  a  want  felt  by  a  writer  who  desired  to  take 
a  class  through  the  history  of  the  great  sculptors  and  painters,  as  a  preliminary  stop  to 
an  intelligent  journey  through  Europe.11— From  Preface. 

For  sale  by  all  booksellers ;  or  sent,  post-paid,  to  any  address  in  the  lifted  States, 
on  receipt  of  price. 

D.  APPLETON  <fe  CO.,  PuUi$hJr9,  Neu  Tort. 


MEMOIRS 


MADAME  DE  REMUSAT, 

1802-1808. 

WITH  PREFACE  AND  NOTES  BY  HER  GRANDSON. 

TRANSLATED  BY 

Mrs,  CASHEL  HOEY  and  JOHN  LILLIE. 


In  three  volumes,  8vo.     Paper,  $1.50  ;  each  volume  separately,  50  cents; 
or  in  one  volume,  12mo,  cloth,  $2.00. 


"The  literary  event  of  the  day,"  remarks  a  Paris  correspondent,  "is  the 
appearance  of  the  'Memoirs  of  Madame  de  Remusat,1  edited  hy  her  grandson, 
Paul  de  Remusat.  Madame  de  Remut-at  was  maid  of  honor  to  Josephine,  with 
whom  she  remained  from  1802  to  1808,  and  so  followed  her  in  her  imperial  for- 
tunes." 

"  It  would  he  easy  to  multiply  quotations  from  this  interesting  hook,  which  no 
one  will  take  up  without  reading  greedily  to  the  end ;  hut  enough  has  heen  said 


'  These  Memoirs  are  unusually  attractive.  As  illustrating  the  interior  history 
of  the  Bonaparte  family,  there  is  hardly  any  book  which  can  equal  them,  while 
the  personality  of  their  writer  is  not  the  least  interesting  revelation." — From 
leading  article  in  the  Daily  News. 

"The  most  fascinating  personal  narrative  which  has  been  published  since 
Madame  d'Arblay's  Memoirs." — May/air. 

"These  Memoirs  are  not  only  a  repository  of  anecdotes  and  of  portraits 
sketched  from  life  by  a  keen-eyed,  quick-witted  woman ;  some  of  the  author's 
reflections  on  social  and  political  questions  are  remarkable  for  weight  and  pene- 
tration."— New  York  Sun. 

"To  thoughtful  readers  the  most  entertaining  as  well  as  the  most  valuable 
parts  of  the  book  are  those  which  graphically  and  piquantly  depict  traits  of 
character,  manners,  and  life,  and  of  such  things  this  work  is  fall.''— 2fel0  York 
Evening  Post. 

"It  brings  into  broad  relief  the  smallnesses  of  the  great  Napoleon  ;  the  in- 
trigues and  scandals  of  court-life  under  the  First  Empire ;  the  jealousies  of  the 
Bonapartes  of  Josephine  and  her  family;  the  listlessness  and  indolent  character 
of  the  latter,  and  the  base  uses  employed  by  Napoleon  to  subordinate  all  around 
him  to  his  will."— New  York  Commercial  Advertiser. 

"No  book  of  the  year  is  calculated  to  create  the  sensation  that  this  will.  It 
is  from  the  pen  of  an  observer  who  writes  of  what  she  knew  and  saw  and 
heard."— Brooklyn  Daily  Union-Argw. 

"Notwithstanding  the  enormous  library  of  works  relating  to  Napoleon,  we 
know  of  none  which  cover  precisely  the  ground  of  these  Memoir?.  Madame 
de  Remnsat  was  not  only  lady-in-waiting  to  Josephine  during  the  eventful 
years  1802-1808,  hut  was  her  intimate  friend  and  trusted  confidant.  Thus  we  get 
a  view  of  the  daily  life  of  Bonaparte  and  his  wife  and  the  terms  on  which  they 
lived  not  elsewhere  to  be  found."— New  York  Mail. 

D.  APPLETON  &  CO.,  Publishers, 

1,  3,  &  5  BOXD  ST.,  NEW  YORK. 


PEOGEESS  AID  POYEETY, 

A  A'   INQUIRY  INTO  THE   CAUSE  OF  INDUSTRIAL  DE- 
PRESSIONS,   AND    OF   INCREASE    OF    WANT 
WITH  INCREASE  OF  WEALTH:    THE 
REMEDY. 

By  HENI^Y   GEORGE. 


One  vol.,  12mo,  512  pages.    Cloth.      •      •      Price,  $2.00. 

From  The  Popular  Science  Monthly. 

"In  'Progress  and  Poverty '  Mr.  Henry  George  has  made  a  careful  and  sys- 
tematic inquiry  into  the  conditions  of  the  production  and  distribution  of  wealth, 
the  relations  of  labor  and  capital,  and  has  traced  out  the  action  of  what  he  con- 
siders the  cause  of  the  continued  association  of  poverty  with  advancing  wealth. 
However  unpalatable  its  conclusions  to  certain  large  classes  of  the  community, 
this  book  must,  from  its  clearness  of  statement,  ingenuity  of  argument,  its  large 
human  sympathy,  aud  the  broad  and  philosophic  spirit  with  which  the  question 
is  treated,  claim  the  attention  of  all  who  realize  the  paramount  importance  of 
the  subject  and  the  value  of  a  thoughtful  contribution  toward  its  elucidation.  .  .  . 
I  am  not  here  concerned  with  criticising  Mr.  George's  work:  my  purpose  is  served 
if  I  have  succeeded  in  drawing  attention  to  what  seems  to  me  one  of  the  most 
important  contributions  yet  made  to  economic  literature. 

"  G.  M.  LTJNGREN." 
From  the  New  York  Sun. 

"  Let  us  say,  at  the  outset,  that  this  is  not  a  work  to  be  brushed  aside  with 
lofty  indifference  or  cool  disdain.  It  is  not  the  production  of  a  visionary  or  a 
sciolist,  of  a  meagerly-equipped  and  ill -regulated  mind.  The  writer  has  brought 
to  his  undertaking  a  comprehensive  knowledge  cf  the  data  and  principles  of 
science,  and  hie  skill  in  exposition  and  illustration  attests  a  broad  acquaintance 
with  history  and  literature.  His  book  must  be  accounted  the  first  adequate  pres- 
entation in  the  English  lansnase  of  that  new  economy  which  has  found  powerful 
champions  in  the  German  universities,  and  which  aims  at  a  radical  transfor- 
mation of  the  science  formulated  by  Adam  bmith.  Ricardo,  and  J.  S.  Mill.  The 
author  does  not  expect  the  scheme  which  he  propounds  in  this  remarkable  book 
to  gain  a  ready  acquiescence :  he  will  doubtless  be  content  if  it  secures  a  patient 
and  respectful  hearing.  This  much  he  unquestionably  deserves.  Few  books 
have,  in  recent  years,  proceeded  from  any  American  pen  which  have  more 
plainly  borne  the  marks  of  wide  learning  and  strenuous  thought,  or  which  have 
brought  to  the  expounding  of  a  serious  theme  a  happier  faculty  of  elucidation. 
A  large  class  of  readers,  who  are  too  often  repelled  from  the  study  of  social  ques- 
tions by  an  abstract  and  technical  mode  of  treatment,  will  be  attracted  to  this 
volume  by  the  brisk,  transparent  style,  by  the  author's  command  of  fresh  meta- 
phor and  simile,  by  the  affluence  of  concrete  facts  and  homely  illustrations.  Nor 
will  any  reader,  we  imagine,  lay  aside  this  book  without  a  haunting  sense  of  the 
breadth  and  urgency  of  the  problem  here  examined.  He  may  not.  indeed,  ac- 
cept the  solution  propounded,  but  he  will  not  reject  it  without  grave  delibera- 
tion ;  or,  we  venture  to  affirm,  without  a  twinge  of  misgiving  and  regret." 

From  the  Chicago  Tribune. 

"Mr.  George's  book  is  welcome,  because  it  will  cause  a  discussion  of  a  sub- 
ject the  magnitude  and  importance  of  which  none  will  deny.  It  is  a  bold  and 
frank  exposition  of  theories  now  forcing  themselves  upon  the  public  notice: 
moreover,  the  writer  is  in  earnest,  and  he  is  also  original." 

D.  APPLETON  &  CO.,  PUBLISHERS,  1,  3,  &  5  BOND  ST.,  NEW  YORK. 


IMPORTANT  WORKS. 


I. 

The   Life   and  Words  of   Christ.     By  CUNNINGHAM  GEIKIE, 
D.  D.     New  cheap  edition.     From  the  same  stereotype  plates  as  the 
two-volume  illustrated  edition.     8vo.     1,258  pages.     Cloth,  $1.50. 
This  edition  of  Geikie's  Life  of  Christ  is  the  only  cheap  edition  that  contains  the 
copious  notes  of  the  author,  ttie  marginal  references,  and  an  index.    Considering  the 
large  type  and  the  ample  page,  the  volume  is  a  marvel  of  cheapness.    It  brings  Dr. 
Geikie's  famous  work,  in  excellent  form,  within  the  reach  of  every  Christian  family  in 
the  land. 

II. 

Ceremonial  Institutions.  Being  Part  IV.  of  "The  Principles 
of  Sociology."  (The  first  portion  of  Volume  II.)  By  HERBERT 
SPENCER.  12mo.  Cloth.  Price,  $1.25. 

"In  this  installment  of 'The  Principles  of  Sociology'  Mr.  Herbert  Spencer  gives  us 
a  monograph  complete  in  itself,  of  moderate  length,  and  on  a  subject  which  affords 
considerable  literary  opportunities.  The  opportunities  have  been  well  used,  and  it 
needs  no  historical  enthusiasm  for  primitive  humanity  to  find  the  book  as  entertaining 
as  it  is  instructive.  ...  The  leading  idea  which  Mr.  Spencer  develops  and  illustrates 
all  through  the  book  is  that,  in  the  early  history  of  society  and  institutions,  form  has 
gone  before  substance." — Saturday  Review. 

III. 

The  Memoirs  of  Madame  ds   Remusat.    1802-1808. 

With  a  Preface  and  Notes  by  her  Grandson,  PAUL  DE  REMUSAT, 
Senator.  In  three  volumes,  8vo,  paper  covers,  price,  $1.50. 

"  In  appreciating  the  character  and  the  policy  of  the  most  remarkable  man  of  mod- 
ern times,  Madame  de  Eemusat  is  likely  to  remain  one  of  the  principal  authorities."— 
London  Athenaeum. 

IV. 

The  Life  of  David  Glasgow  Farragut,  First  Admiral  of 

the  United  States  Navy,  embodying  his  Journal  and  Letters.  By 
his  Son,  LOYALL  FARRAGUT.  With  Portraits,  Maps,  and  Illustra- 
tions. 8vo.  Cloth.  Price,  $4.00. 

"The  book  is  a  stirring  one,  of  course;  the  story  of  Farragut's  life  is  a  tale  of 
adventure  of  the  most  ravishing  sort,  so  that,  aside  from  the  value  of  this  work  as  an 
authentic  biography  of  the  greatest  of  American  naval  commanders,  the  book  is  one  of 
surpassing  interest,  considered  merely  as  a  narrative  of  difficult  and  dangerous  enter- 
prises and  heroic  achievements." — New  York  Evening  Post. 

V. 

The  Crayfish.  AN  INTRODUCTION  TO  THE  STUDY  OF  ZO- 
OLOGY. By  Professor  T.  H.  HCXLEY,  F.  R.  S.  With  82  Illustra- 
tions. Forming  Volume  28  of  "  The  International  Scientific  Series." 
12mo.  Cloth.  Price,  $1.75. 

The  book  is  termed  an  "Introduction  to  Zoology."  "For  whoever  will  follow  its 
pages,  crayfish  in  hand,  and  will  try  to  verify  for  himself  the  statements  which  it  con- 
tains, will  find  himself  brought  face  to  face  with  all  the  great  zoological  questions  which 
excite  s«  lively  an  interest  at  the  present  day." 

D.  APPLETON  &  CO.,  PUBLISHERS,  1,  3,  &  5  BOND  ST.,  NEW  YORK 


WORKS  OF  H.  ALLEYNE  NICHOLSON,  M.D. 


I. 

Text-Book   Of  Zoology,  for  Schools  and  Col- 
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H. 

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with  a  General  Introduction  to  the  Principles  of  Zoology.  Sec- 
ond edition.  Revised  and  enlarged,  with  243  Woodcuts.  12mo. 
Cloth,  $2.50. 

in. 

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leges.    12mo.     Half  roan,  $1.30. 

IV. 

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Illustrated.     12mo.     Cloth,  65  cents. 


The    Ancient    Life  -History   of    the 

Eartl\.      A  Comprehensive  Outline  of  the  Principles  and  Lead- 
ing Facts  of  Palaeontological  Science.     12mo.     Cloth,  $2.00. 

The  Quarterly  Journal  of  Science. 

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every  phenomenon  which  he  records,  and  knows  how  to  make  it  reveal  its  les- 
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book of  the  historical  phase  of  palaeontology  it  will  be  indispensable  to  students, 
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pires even  to  an  outline  knowledge  of  natural  science  can  deem  his  library  com- 
plete." 

Athenaeum. 

"The  Professor  of  Natural  History  in  the  University  of  St.  Andrews  has.  by 


his  previous  works  on  zoSlogy  and  palaeontology,  so  fully  established  his  claim 
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